全文获取类型
收费全文 | 15291篇 |
免费 | 1208篇 |
国内免费 | 54篇 |
专业分类
耳鼻咽喉 | 208篇 |
儿科学 | 322篇 |
妇产科学 | 215篇 |
基础医学 | 1912篇 |
口腔科学 | 430篇 |
临床医学 | 1532篇 |
内科学 | 3571篇 |
皮肤病学 | 187篇 |
神经病学 | 1199篇 |
特种医学 | 635篇 |
外科学 | 2292篇 |
综合类 | 316篇 |
一般理论 | 16篇 |
预防医学 | 1153篇 |
眼科学 | 502篇 |
药学 | 1045篇 |
中国医学 | 38篇 |
肿瘤学 | 980篇 |
出版年
2022年 | 81篇 |
2021年 | 191篇 |
2020年 | 96篇 |
2019年 | 191篇 |
2018年 | 215篇 |
2017年 | 167篇 |
2016年 | 204篇 |
2015年 | 250篇 |
2014年 | 397篇 |
2013年 | 665篇 |
2012年 | 823篇 |
2011年 | 895篇 |
2010年 | 491篇 |
2009年 | 472篇 |
2008年 | 875篇 |
2007年 | 994篇 |
2006年 | 1014篇 |
2005年 | 983篇 |
2004年 | 1044篇 |
2003年 | 957篇 |
2002年 | 970篇 |
2001年 | 137篇 |
2000年 | 94篇 |
1999年 | 168篇 |
1998年 | 230篇 |
1997年 | 205篇 |
1996年 | 181篇 |
1995年 | 193篇 |
1994年 | 145篇 |
1993年 | 150篇 |
1992年 | 89篇 |
1991年 | 95篇 |
1990年 | 98篇 |
1989年 | 96篇 |
1988年 | 100篇 |
1987年 | 78篇 |
1986年 | 86篇 |
1985年 | 113篇 |
1984年 | 168篇 |
1983年 | 147篇 |
1982年 | 217篇 |
1981年 | 217篇 |
1980年 | 164篇 |
1979年 | 90篇 |
1978年 | 113篇 |
1977年 | 143篇 |
1976年 | 136篇 |
1975年 | 121篇 |
1974年 | 95篇 |
1973年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
101.
An atypical pre-β-lipoprotein of human serum has been detected by agarose gel electrophoresis in four patients, three of whom were siblings. This lipoprotein differed from the pre-β lipoprotein previously observed with this technique by sedimenting on ultracentrifugation at density 1.006. 相似文献
102.
Gluthatione-S-transferase P1 polymorphism I105V in familial and sporadic prostate cancer 总被引:1,自引:0,他引:1
Debes JD Yokomizo A McDonnell SK Hebbring SJ Christensen GB Cunningham JM Jacobsen SJ Tindall DJ Liu W Schaid DJ Thibodeau SN 《Cancer Genetics and Cytogenetics》2004,155(1):82-86
Several reports suggest that the glutathione-S-transferase (GST) family of enzymes is involved in a variety of cancers, due to their carcinogen-detoxification properties. A polymorphism in codon 105 of the pi variant (GSTP1 I105V), which affects the enzymatic activity of the enzyme, has been linked to the incidence of cancers from different organs. However, the published data in prostate cancer (PCa) is controversial. Some studies report an association with the GSTP1 I105V polymorphism and sporadic PCa, whereas other studies report no association. Recently, one study showed a positive correlation between the GSTP1 I105V polymorphism and familial PCa in a Japanese population. In the present study, we assessed the correlation of the GSTP1 I105V polymorphism with familial and sporadic PCa in an American population. We analyzed DNA samples from 438 patients with familial PCa, 499 patients with sporadic PCa, and 510 controls. We found no significant association between the GSTP1 I105V polymorphism and familial or sporadic PCa when compared to the control group [odds ratio (OR) =1.0 (0.74-1.37); P=0.58]. Moreover, no association was found after stratification for age of diagnosis, Gleason grade, or lymph node involvement [OR =0.84 (0.65-1.09), P=0.37]. These data indicate that there is no associated risk for sporadic or familial PCa in American families containing the GSTP1 I105V polymorphism. 相似文献
103.
Spontaneously occurring urinary tract infection (UTI) in dogs was exploited as an experiment of nature to gain insights into UTI pathogenesis in humans. Concurrent urinary and rectal Escherichia coli isolates from 37 dogs with UTI were compared with respect to phylogenetic background, O antigens, and extended virulence genotype. In 54% of the UTI episodes, the dog's urinary and rectal isolates represented the same strain. Urinary isolates differed dramatically from rectal-only isolates in that they derived predominantly from E. coli phylogenetic group B2, expressed typical (human) UTI-associated O antigens, and possessed many virulence-associated genes, most notably pap elements (P fimbriae), papG (adhesin) allele III, sfa/foc and sfaS (S fimbriae), hly (hemolysin), fyuA (yersiniabactin), iroN (siderophore), and ompT (outer membrane protease T). The 20 urinary isolates that corresponded with the host's predominant rectal strain were no less virulent according to the markers analyzed than were the 17 urinary isolates that differed from the host's predominant rectal strain. These findings suggest that UTI pathogenesis is similar in dogs and humans, provide added support for the special-pathogenicity over the prevalence hypothesis of UTI pathogenesis, and identify numerous specific virulence-associated factors as significant correlates of urovirulence. 相似文献
104.
Lung epithelial cells and extracellular matrix components induce expression of Pneumocystis carinii STE20, a gene complementing the mating and pseudohyphal growth defects of STE20 mutant yeast
下载免费PDF全文
![点击此处可从《Infection and immunity》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Pneumocystis carinii causes severe pneumonia in immunocompromised hosts. The binding of P. carinii to alveolar epithelial cells and extracellular matrix constituents such as fibronectin and vitronectin is a central feature of infection, which initiates proliferation of the organism. Herein, we demonstrate that P. carinii binding to lung cells specifically alters the gene expression of the organism, regulating fungal growth. Subtractive hybridization was performed to isolate P. carinii genes expressed following binding to mammalian extracellular matrix constituents. P. carinii STE20 (PCSTE20), a gene participating in mating and pseudohyphal growth of other fungi, was identified following adherence to the extracellular matrix constituents fibronectin, vitronectin, collagen, and lung epithelial cells. The expression of PCSTE20 and a related P. carinii mitogen-activated protein kinase (MAPK) kinase gene, also implicated in signaling of mating, were both specifically upregulated by binding to matrix protein. The expression of general cyclin-dependent kinases and other MAPKs not involved in mating pathways were not altered by organism binding. PCSTE20 expression was also strongly enhanced following organism attachment to A549 lung epithelial cells. When expressed in a Saccharomyces cerevisiae ste20Delta mutant, PCSTE20 suppressed defects in both mating and pseudohyphal growth. These findings are consistent with the observed proliferation and filopodial extension of Pneumocystis organisms adherent to the epithelium in the lungs of immunocompromised hosts. PCSTE20 expression appears to represent a significant component in the regulation of the life cycle of this intractable opportunistic pathogen. 相似文献
105.
Single-Step Multiplex PCR Assay for Characterization of New World Leishmania Complexes 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Journal of clinical microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Eva Harris Gerald Kropp Alejandro Belli Betzab Rodriguez Nina Agabian 《Journal of clinical microbiology》1998,36(7):1989-1995
We have developed a PCR assay for one-step differentiation of the three complexes of New World Leishmania (Leishmania braziliensis, Leishmania mexicana, and Leishmania donovani). This multiplex assay is targeted to the spliced leader RNA (mini-exon) gene repeats of these organisms and can detect all three complexes simultaneously, generating differently sized products for each complex. The assay is specific to the Leishmania genus and does not recognize related kinetoplastid protozoa, such as Trypanosoma cruzi, Trypanosoma brucei, and Crithidia fasciculata. It correctly identified Leishmania species with a broad geographic distribution in Central and South America. The sensitivity of the PCR amplification ranged from 1 fg to 10 pg of DNA (0.01 to 100 parasites), depending on the complex detected. Crude extracts of cultured parasites, prepared simply by boiling diluted cultures, served as excellent templates for amplification. Crude preparations of clinical material were also tested. The assay detected L. braziliensis in dermal scrapings from cutaneous leishmanial lesions, Leishmania chagasi in dermal scrapings of atypical cutaneous leishmaniasis, and L. mexicana from lesion aspirates from infected hamsters. We have minimized the material requirements and maximized the simplicity, rapidity, and informative content of this assay to render it suitable for use in laboratories in countries where leishmaniasis is endemic. This assay should be useful for rapid in-country identification of Leishmania parasites, particularly where different Leishmania complexes are found in the same geographical area. 相似文献
106.
The dynamic behavior of a batch culture of yeast with a rate-limiting nutrient was analyzed by examining the cell number density, cell size distribution, and concentration of a rate-limiting nutrient. The particular strain of S. cerevisiae studied grows only when the medium contains L-tryptophan. The cell number, volume distribution, and external L-tryptophan concentration were measured at successive times in the development of the culture. A mathematical model was developed to simulate the experimental data and provide a framework for understanding the dynamics of the cell growth and division in terms of cellular events. A nonlinear optimization procedure was specially adapted to estimate model parameters. 相似文献
107.
Gerald L. Stoner 《Brain pathology (Zurich, Switzerland)》1993,3(3):213-227
Multiple sclerosis (MS) is generally considered to be an autoimmune disorder with myelin as the target and with several unidentified viruses playing ancillary roles, possibly through molecular mimicry. Although this paradigm has led to important progress on potential mechanisms of myelin loss, neither a target antigen in myelin nor a triggering mechanism has yet been identified, leaving the etiology of MS still unknown. Animal models of viral demyelination and studies showing that JC virus (JCV), the polyomavirus which causes progressive multifocal leukoencephalopathy (PML), may be latent in some normal human brains suggest another possibility. A host immune response targeting proteins expressed at low levels from viral DNA latent in the central nervous system (CNS) might underlie a focal demyelinating disease such as MS. A shift from autoimmunity to a latent-virus model is not a trivial substitution of target antigens. This shift would expand the search for a definitive laboratory test for MS and could lead to improved therapeutic and preventive approaches. 相似文献
108.
109.
The effect of direct intrahypothalamic nitric oxide (NO) administration on the release of selected amino acids in the hypothalamic supraoptic nucleus (SON) with and without concomitant forced swimming was investigated. Adult male Wistar rats were chronically fitted with U-shaped microdialysis probes in the SON and forced to swim for 10-min in 20-degree C warm water. Thirty-min microdialysis samples were collected before, during and after the forced swimming period while NO was administered into the SON via microdialysis. The results show that NO administration in combination with forced swimming affects the release of aspartate, glutamate, taurine, and gamma aminobutyric acid (GABA) in different patterns. Whereas the release of the excitatory amino acids aspartate and glutamate was triggered only during NO administration and forced swimming, the inhibitory amino acids GABA and taurine were found in the extracellular fluid in increased concentrations also after the treatment. These data indicate that NO administration differently affects the release of excitatory and inhibitory amino acids within the SON. Thus, SON neurons which contain high concentrations of neuronal NO synthase, might contribute to the regulation of their own secretory activity by releasing NO that controls the orchestrated release of excitatory and inhibitory amino acids from axon terminals of afferences and interneurons as well as release from glial cells. 相似文献
110.
Recent experiments have shown that shortening and stretching of sarcomeres in single activated and unactivated myofibrils occur in stepwise fashion (Yang et al. (1998) Biophys J 74: 1473-1483; Blyakhman et al. (2001) Biophys J 81: 1093-1100; Yakovenko et al. (2002) Am J Physiol Cell Physiol 283: 735-742). Here, we carried out measurements on single myofibrils from rabbit psoas muscle to investigate steps in unactivated specimens in more detail. Activated and unactivated myofibrils were released and stretched in ramp-like fashion. The time course of length change in the single sarcomere was consistently stepwise. We found that in the unactivated myofibrils, step size depended on initial sarcomere length, diminishing progressively with increase of initial sarcomere length, whereas in the case of activated sarcomeres, step size was consistently 2.7 nm. 相似文献