全文获取类型
收费全文 | 158205篇 |
免费 | 11105篇 |
国内免费 | 621篇 |
专业分类
耳鼻咽喉 | 1764篇 |
儿科学 | 3919篇 |
妇产科学 | 2612篇 |
基础医学 | 20937篇 |
口腔科学 | 3393篇 |
临床医学 | 15538篇 |
内科学 | 33528篇 |
皮肤病学 | 3250篇 |
神经病学 | 14584篇 |
特种医学 | 6959篇 |
外国民族医学 | 14篇 |
外科学 | 25204篇 |
综合类 | 1953篇 |
一般理论 | 109篇 |
预防医学 | 11758篇 |
眼科学 | 3300篇 |
药学 | 10133篇 |
中国医学 | 238篇 |
肿瘤学 | 10738篇 |
出版年
2023年 | 807篇 |
2022年 | 1242篇 |
2021年 | 3373篇 |
2020年 | 2079篇 |
2019年 | 3118篇 |
2018年 | 3591篇 |
2017年 | 2799篇 |
2016年 | 3135篇 |
2015年 | 3586篇 |
2014年 | 5097篇 |
2013年 | 6852篇 |
2012年 | 10338篇 |
2011年 | 11004篇 |
2010年 | 6310篇 |
2009年 | 6018篇 |
2008年 | 9746篇 |
2007年 | 10187篇 |
2006年 | 10095篇 |
2005年 | 10143篇 |
2004年 | 9307篇 |
2003年 | 8617篇 |
2002年 | 8267篇 |
2001年 | 2149篇 |
2000年 | 1840篇 |
1999年 | 2128篇 |
1998年 | 1931篇 |
1997年 | 1557篇 |
1996年 | 1342篇 |
1995年 | 1255篇 |
1994年 | 1128篇 |
1993年 | 1017篇 |
1992年 | 1294篇 |
1991年 | 1190篇 |
1990年 | 1033篇 |
1989年 | 972篇 |
1988年 | 918篇 |
1987年 | 886篇 |
1986年 | 885篇 |
1985年 | 869篇 |
1984年 | 927篇 |
1983年 | 797篇 |
1982年 | 962篇 |
1981年 | 869篇 |
1980年 | 731篇 |
1979年 | 656篇 |
1978年 | 646篇 |
1977年 | 535篇 |
1976年 | 515篇 |
1974年 | 512篇 |
1973年 | 450篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
991.
Thomas R. Kozel Bouke C. H. deJong Matthew M. Grinsell Randall S. MacGill Kevin K. Wall 《Infection and immunity》1998,66(4):1538-1546
Incubation of the encapsulated yeast Cryptococcus neoformans in human serum leads to alternative pathway-mediated deposition of C3 fragments in the capsule. We examined the ability of monoclonal antibodies (MAbs) specific for different epitopes of the major capsular polysaccharide to alter the kinetics for classical and alternative pathway-mediated deposition of C3 onto a serotype A strain. We studied MAbs reactive with capsular serotypes A, B, C, and D (MAb group II); serotypes A, B, and D (MAb group III); and serotypes A and D (MAb group IV). The MAb groupings are based on antibody variable region usage which determines the antibody molecular structure. When both the classical and alternative pathways were operative, group II MAbs induced early classical pathway-mediated binding of C3 but reduced the overall rate of C3 accumulation and the amount of bound C3. Group III MAbs closely mimicked the effects of group II MAbs but exhibited reduced support of early classical pathway-facilitated accumulation of C3. Depending on the antibody isotype, group IV MAbs slightly or markedly enhanced early binding of C3 but had no effect on either the rate of C3 accumulation or the amount of bound C3. When the classical pathway was blocked, group II and III MAbs markedly suppressed C3 binding that normally would have occurred via the alternative pathway. In contrast, MAbs of group IV had no effect on alternative pathway-mediated C3 binding. These results indicate that anticapsular antibodies with different epitope specificities may have distinct regulatory effects on activation and binding of C3.Cryptococcus neoformans is the etiological agent of cryptococcal meningitis, a life-threatening infection of particular importance in patients with deficiencies in cellular immunity, most notably patients with the AIDS. The yeast is surrounded by a polysaccharide capsule that is composed primarily of glucuronoxylomannan (GXM), which has a linear (1→3)-α-d-mannopyranan backbone bearing β-d-xylopyranosyl, β-d-glucopyranosyluronic acid, and O-acetyl substituents (3, 9, 54). The cryptococcal capsule occurs as four major serotypes (A, B, C, and D) and is an essential virulence factor for the yeast.One of the most striking features of the cryptococcal capsule is its ability to activate the alternative complement pathway. Incubation of encapsulated cryptococci in normal human serum (NHS) leads to the deposition of 107 to 108 C3 fragments on the yeast (28, 56). The C3 is deposited at the surface and throughout the capsule (30). Available evidence indicates that the amount of anti-GXM antibodies found in NHS is not sufficient to initiate the classical pathway (24); consequently, activation and binding of C3 to the cryptococcal capsule are mediated entirely by the alternative complement pathway (29, 30, 55). One of the hallmark features of alternative pathway deposition of C3 onto encapsulated cryptococci is a delay of 5 to 8 min before readily detectable amounts of C3 are found on yeast cells incubated in NHS (29, 55). Once past the initial lag, C3 fragments rapidly accumulate on the yeast cells as incubation proceeds for an additional 10 min.Recently, there has been interest in antibody-mediated resistance to cryptococcosis. Monoclonal antibodies (MAbs) have been proposed for treatment of cryptococcosis (7), and immunization with GXM-protein conjugates has been suggested for prevention of cryptococcosis (6, 12, 13). However, it is becoming increasingly clear that anti-GXM MAbs may have distinct specificities and biological activities. Anti-GXM MAbs which differ in (i) reactivities with GXM of the four major serotypes (2), (ii) apparent binding sites in the cryptococcal capsule (32, 37), and (iii) abilities to provide protection in a murine model of cryptococcosis (32, 37) have been described. Some differences in biological activity are related to differences in the epitope specificities of the various MAbs (32, 37).One means by which antibodies could enhance resistance to cryptococcosis is through accelerated deposition of opsonic C3 fragments via the action of the classical pathway. Such an acceleration would reduce or eliminate the 5- to 8-min lag that occurs during alternative pathway-mediated deposition of C3 fragments. The objectives of our study were to evaluate the effects of anti-GXM MAbs on the kinetics and sites for deposition of C3 fragments into the cryptococcal capsule. We examined several well-characterized antibodies that differed in the epitope specificity of the MAbs. The results showed that MAbs with different isotypes and epitope specificities had distinctly different effects on activation and binding of C3 via the classical and alternative pathways; many antibodies markedly suppressed C3 binding, some antibodies accelerated C3 binding, and other antibodies had little or no effect. 相似文献
992.
Merkler D Boretius S Stadelmann C Ernsting T Michaelis T Frahm J Brück W 《NMR in biomedicine》2005,18(6):395-403
Although magnetic resonance imaging (MRI) represents the most sensitive tool for the detection of white matter abnormalities in patients with multiple sclerosis (MS), the heterogeneity of MS placques severely hampers the elucidation of specific pathophysiological processes. In order to identify putative MRI markers for de- and remyelination, we employed the cuprizone mouse model which leads to a selective and reversible demyelination of the corpus callosum with little or no axonal damage. Apart from histopathology, animals were studied with high-resolution three-dimensional MRI in vivo using multiple contrasts. While individual MRI findings significantly correlated with electron microscopy, the differentiation of regions with normal, demyelinated or remyelinated white matter by one contrast alone was less specific than by histology or electron microscopy. However, an accurate MRI prediction of the in vivo myelin status was achieved by a discriminant function analysis using a combination of T1, T2 and magnetization transfer contrast. With a correct assignment of 95% of all animals examined, the procedure will allow for the survey of new therapeutic approaches aiming at improved remyelination. 相似文献
993.
Effects of tibolone on bone quality in ovariectomized monkeys 总被引:1,自引:0,他引:1
OBJECTIVE: The purpose of this report is to examine the effects of two doses of tibolone on bone quality (bone biomarkers, bone density, and bone strength) in ovariectomized cynomolgus monkeys fed high-fat diets. DESIGN: Ovariectomized cynomolgus monkeys were randomized into one of five treatment groups: placebo-treated control, tibolone (0.2 mg/kg/day), tibolone (0.05 mg/kg/day), conjugated equine estrogens (Premarin, 0.042 mg/kg/day), and conjugated equine estrogens plus medroxyprogesterone acetate (0.042 and 0.167 mg/kg/day, respectively). Bone quality was assessed by determining bone strength and density in vertebrae and femora collected after 24 months of treatment. RESULTS: Monkeys treated for 24 months with tibolone had increased bone mineral density in the distal femur and improved biomechanical properties in the midshaft femur compared with placebo-treated ovariectomized monkeys, as did monkeys treated with conjugated equine estrogens with or without medroxyprogesterone acetate. No treatment effects were seen in lumbar vertebra bone density or strength. There was no significant difference between tibolone and estrogen on biomechanical properties of the femur. CONCLUSION: These data show that tibolone is comparable to conjugated equine estrogens with or without medroxyprogesterone acetate in decreasing bone turnover and increasing bone strength in ovariectomized monkeys. 相似文献
994.
995.
Hantavirus Pulmonary Syndrome: Pathogenesis of an Emerging Infectious Disease 总被引:23,自引:1,他引:23 下载免费PDF全文
Sherif R. Zaki Patricia w. Greer Lisa M. Coffield Cynthia S. Goldsmith Kurt B. Nolte Kathy Foucar Richard M. Feddersen Ross E. Zumwalt Gayle L. Miller Ali S. Khan Pierre E. Rollin Thomas G. Ksiazek Stuart T. Nichol Brian W.J. Mahy Clarence J. Peters 《The American journal of pathology》1995,146(3):552-579
996.
Michael Z. Gilcrease MD PhD Laura Schmidt PhD Berton Zbar MD Luan Truong MD Michael Rutledge MD Thomas M. Wheeler MD 《Human pathology》1995,26(12)
Papillary cystadenoma of the epididymis is an uncommon benign lesion that may occur sporadically or as a manifestation of von Hippel—Lindau (VHL) disease. Neither immunohistochemical studies nor molecular genetic analyses of the VHL gene have been reported previously for this lesion. The authors describe two cases of clear cell papillary cystadenoma of the epididymis, both of which were initially confused with metastatic renal cell carcinoma. Both lesions showed positive immunohistochemical staining for low and intermediate molecular weight keratins (Cam 5.2 and AE1/AE3), EMA, vimentin, α1-antitrypsin, and α1-antichymotrypsin. Each was negative for CEA. Because clear cell papillary cystadenoma is similar to renal cell carcinoma histologically, and because both occur as components of the von Hippel—Lindau disease complex, the authors analyzed both cases for the presence of mutations in the VHL gene. A somatic VHL gene mutation was detected in one of the two tumors by polymerase chain reaction followed by single-strand conformation polymorphism analysis. Direct sequencing revealed a cytosine to thymine transition at nucleotide 694, resulting in the replacement of an arginine with a stop codon after the sixth amino acid of exon 3. As the VHL gene is believed to function as a tumor suppressor gene, VHL gene mutations may play a role in the initiation of tumorigenesis in sporadic cystadenomas of the epididymis. 相似文献
997.
P. Mrel K. Hoang-Xuan M. Sanson A. Moreau-Aubry E. K. Bijlsma C. Lazaro J. P. Moisan F. Resche I. Nishisho X. Estivill J. Y. Delattre M. Poisson C. Theillet T. Hulsebos O. Delattre G. Thomas 《Genes, chromosomes & cancer》1995,13(3):211-216
The NF2 gene is a putative tumor-suppressor gene that, when it is altered in the germline, causes neurofibromatosis type 2, a tumor-susceptibility disease that mainly predisposes to schwannomas and meningiomas. The recent isolation of the NF2 gene on chromosome 22 allows the identification of somatic mutations in human tumors. We have searched for mutations of the NF2 gene in 331 primary human tumors using a screening method based on denaturing gradient gel electrophoresis, which allows the detection of mutations in 95% of the coding sequence. Mutations were observed in 17 of 57 meningiomas and in 30 of 89 schwannomas. No mutations were observed for 17 ependymomas, 70 gliomas, 23 primary melanomas, 24 pheochromocytomas, 15 neuroblastomas, 6 medulloblastomas, 15 colon cancers, and 15 breast cancers. All meningiomas and one-half of the schwannomas with identified NF2 mutations demonstrated chromosome 22 allelic losses. We conclude that the involvement of the NF2 gene in human tumorigenesis may be restricted to schwannomas and meningiomas, where it is frequently inactivated by a two-hit process. © 1995 Wiley-Liss, Inc. 相似文献
998.
This report details the fine-needle aspiration biopsy (FNAB) cytomorphologic features of two cases of salivary gland mycosis. Both patients had acquired immunodeficiency syndrome (AIDS) and presented with parotid gland masses. The first patient had Histoplasmosis with secondary infection by Candida. Cytopathologically, the FNAB smears showed classic features of a deep-seated mycosis characterized by necrosis and scattered fungal forms. The second patient had a colonizing sialadenitis caused by either Asperigillus or Fusarium. Cytopathologically, the findings were similar to those seen in aspergillomas of the lung orparanasal sinuses with numerous hyphal forms and an absence of an inflammatory response. Because mycotic disease can induce a wide spectrum of pathogenic change, other benign or malignant, solid or cystic lesions enter into the differential diagnosis. Diagn Cytopathol 1994; 11:286–290. © 1994 Wiley-Liss, Inc. 相似文献
999.
We have used the techniques of DNA fingerprinting and polymerase chain reaction (PCR) with probes specific for hypervariable repetitive DNA sequences (mini- and microsatellite DNAs) to analyze 36 yeast strains belonging to 10 species and 2 genera. Using (GTG)5, (GACA)4, phage M13 DNA and the M13 sequence GAGGGTGGCGGTTCT as probes and primers, respectively, we obtained DNA polymorphisms which allowed us to discriminate 23 biotechnologically important strains of the yeast Saccaromyces cerevisiae and to distinguish them from strains of S. pastorianus, S. bayanus and S. willianus. Our results demonstrate that both DNA and PCR fingerprinting are suitable tools for an easy, fast and reliable molecular typing of yeasts. The DNA fingerprinting method seems to be more sensitive than PCR fingerprinting with respect to the individualization of strains. Nevertheless, using the PCR fingerprinting technique we were able to unambigously dicriminate between yeast genotypes of different species. Therefore, PCR fingerprinting might become a useful tool in the classification of yeasts on the basis of phylogenetic relatedness. 相似文献
1000.
Performance of a commercial, type-specific enzyme-linked immunosorbent assay for detection of herpes simplex virus type 2-specific antibodies in Ugandans 下载免费PDF全文
Laeyendecker O Henson C Gray RH Nguyen RH Horne BJ Wawer MJ Serwadda D Kiwanuka N Morrow RA Hogrefe W Quinn TC 《Journal of clinical microbiology》2004,42(4):1794-1796
Two hundred forty-eight human immunodeficiency virus (HIV)-positive and 496 HIV-negative subjects in Uganda were tested by HerpeSelect herpes simplex virus type 2 enzyme-linked immunosorbent assay (ELISA) and Western blotting to optimize the ELISA for use in this population. A higher index cutoff value was required for optimal sensitivity and specificity, and overall performance of the assay was not affected by HIV status. 相似文献