全文获取类型
收费全文 | 13273篇 |
免费 | 934篇 |
国内免费 | 34篇 |
专业分类
耳鼻咽喉 | 126篇 |
儿科学 | 632篇 |
妇产科学 | 422篇 |
基础医学 | 1797篇 |
口腔科学 | 280篇 |
临床医学 | 1578篇 |
内科学 | 2681篇 |
皮肤病学 | 253篇 |
神经病学 | 1229篇 |
特种医学 | 275篇 |
外国民族医学 | 1篇 |
外科学 | 1293篇 |
综合类 | 239篇 |
一般理论 | 26篇 |
预防医学 | 1444篇 |
眼科学 | 312篇 |
药学 | 756篇 |
中国医学 | 27篇 |
肿瘤学 | 870篇 |
出版年
2023年 | 107篇 |
2022年 | 166篇 |
2021年 | 394篇 |
2020年 | 247篇 |
2019年 | 358篇 |
2018年 | 374篇 |
2017年 | 288篇 |
2016年 | 342篇 |
2015年 | 356篇 |
2014年 | 484篇 |
2013年 | 675篇 |
2012年 | 988篇 |
2011年 | 1032篇 |
2010年 | 597篇 |
2009年 | 537篇 |
2008年 | 824篇 |
2007年 | 907篇 |
2006年 | 787篇 |
2005年 | 764篇 |
2004年 | 709篇 |
2003年 | 640篇 |
2002年 | 640篇 |
2001年 | 134篇 |
2000年 | 119篇 |
1999年 | 135篇 |
1998年 | 115篇 |
1997年 | 93篇 |
1996年 | 81篇 |
1995年 | 90篇 |
1994年 | 71篇 |
1993年 | 59篇 |
1992年 | 77篇 |
1991年 | 73篇 |
1990年 | 59篇 |
1989年 | 62篇 |
1988年 | 59篇 |
1987年 | 52篇 |
1986年 | 47篇 |
1985年 | 62篇 |
1984年 | 48篇 |
1983年 | 56篇 |
1982年 | 41篇 |
1981年 | 44篇 |
1980年 | 35篇 |
1979年 | 38篇 |
1978年 | 43篇 |
1977年 | 42篇 |
1976年 | 35篇 |
1974年 | 28篇 |
1972年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
61.
62.
Arifler D Guillaud M Carraro A Malpica A Follen M Richards-Kortum R 《Journal of biomedical optics》2003,8(3):484-494
The finite-difference time-domain (FDTD) method provides a flexible approach to studying the scattering that arises from arbitrarily inhomogeneous structures. We implemented a three-dimensional FDTD program code to model light scattering from biological cells. The perfectly matched layer (PML) boundary condition has been used to terminate the FDTD computational grid. We investigated differences in angle-dependent scattering properties of normal and dysplastic cervical cells. Specifically, the scattering patterns and phase functions have been computed for normal and dysplastic cervical cells at three different epithelial depths, namely, basal/parabasal, intermediate, and superficial. Construction of cervical cells within the FDTD computational grid is based on morphological and chromatin texture features obtained from quantitative histopathology. The results show that angle-dependent scattering characteristics are different not only for normal and dysplastic cells but also for cells at different epithelial depths. The calculated scattering cross-sections are significantly greater for dysplastic cells. The scattering cross-sections of cells at different depths indicate that scattering decreases in going from the superficial layer to the intermediate layer, but then increases in the basal/parabasal layer. This trend for epithelial cell scattering has also been observed in confocal images of ex vivo cervical tissue. 相似文献
63.
Sj?gren Anita; Hillensj? Torbj?rn; Hamberger Lars 《Human reproduction (Oxford, England)》1987,2(6):469-473
Granulosa cells were aspirated from human pre-ovulatory folliclesfollowing a combined clomiphene-gonadotrophin stimulation inan in-vitro fertilization (IVF) programme. The cells were culturedfor 8 days in medium M199 containing 10% bovine fetal calf serumunder 5% CO2 in air. Pure human FSH and human LH were addedalone or in combination to the culture in various concentrationsand the progesterone (P) and oestradiol-17 (E2) levels in themedium were measured every second day by a conventional RIAtechnique. In the presence of FSH or LH the formation of P increased2- to 3-fold with the pronounced effect after 4 to 6 days inculture. Addition of testosterone (T) (3 ? 107 M) tothe culture medium affected neither basal nor gonadotrophinstimulated P formation. In this system, only minute amountsof E2 were formed and neither FSH nor LH stimulated its formation.When the medium was fortified with T, basal E2 formation increased50- to 100-fold. FSH further stimulated this conversion significantlyafter 6 and 8 days of culture, while LH had no significant influence. 相似文献
64.
65.
Smad4 overexpression causes germ cell ablation and leydig cell hyperplasia in transgenic mice
下载免费PDF全文
![点击此处可从《The American journal of pathology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Narula A Kilen S Ma E Kroeger J Goldberg E Woodruff TK 《The American journal of pathology》2002,161(5):1723-1734
Members of the transforming growth factor-beta (TGF-beta) superfamily play a variety of important roles in testicular development and function. The tumor suppressor gene, Smad4, is a common mediator of TGF-beta, activin, and bone morphogenetic protein-mediated signaling pathways. To investigate the role of the Smad4 gene during testicular development and function, transgenic mice were generated using a Flag-tagged Smad4 gene driven by 180-bp fragment of the Mullerian inhibiting substance upstream promoter sequence. Three Smad4 transgenic founders (A, B, and G) were detected by Southern blot analysis; line B showed the highest expression of the Smad4 transgene and was further studied. The fertility in F1 generation (B) and F2 generation (BB) of the Smad4 transgenic mice was not impaired. However, in the F3 generation (B2x) all animals were impacted by the overexpression of the Smad4 transgene and two kinds of phenotypes were observed. In one group animals were completely infertile, while in the other group animals were fertile and sired the normal number of pups/litter. These groups are designated as infertile and fertile in the text. Histological evaluation of the testes from the infertile group showed variable degrees of Leydig cell hyperplasia, apoptosis of germ cells, spermatogenic arrest, seminiferous tubule degeneration, and infertility. In the fertile group, there was no apparent change in the histology of the testis except for a slight increase in the number of Leydig cells. Serum follicle-stimulating hormone levels in the adult animals of both groups of Smad4 transgenic male mice were not significantly different from normal littermates; however, testosterone levels in both groups were significantly (P < 0.05) increased. These results suggest that overexpression of Smad4 leads to testicular abnormalities and infertility supporting the hypothesis that the TGF-beta signaling pathways are carefully orchestrated during testicular development. In the absence of normal levels of Smad4 testicular function is compromised. 相似文献
66.
Pneumococcal surface protein A is expressed in vivo, and antibodies to PspA are effective for therapy in a murine model of pneumococcal sepsis
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)
Pneumococcal surface protein A (PspA) is an immunogenic protein expressed on the surface of all strains of Streptococcus pneumoniae (pneumococcus) and induces antibodies which protect against invasive infection in mice. Pneumococci used for infectious challenge in protection studies are typically collected from cultures grown in semisynthetic medium in vitro. The purpose of these studies is to confirm that PspA is expressed by pneumococci during growth in vivo at a level sufficient for antibodies to PspA to be protective. Mice were actively immunized with purified PspA or by passive transfer of monoclonal antibody (MAb) and challenged with a capsular type 3 strain in diluted whole blood from bacteremic mice. All were protected against challenge with 10 times the 50% lethal dose (LD(50)), and mice challenged with 1,000 times the LD(50) had increased survival compared with controls. Additionally, nonimmune mice treated with MAbs to PspA or PspA immune serum at 6 and 12 h after infection with 10 times the LD(50) also showed increased survival. Northern blot analysis of RNA from pneumococci grown either in vitro or in vivo showed similar levels of PspA mRNA. These results demonstrate that PspA is expressed in vivo in a mouse model and that immunization with PspA induces antibodies to an antigen which is expressed during the course of invasive infection. Immunotherapy with antibodies to PspA may have some utility in treating pneumococcal infections in humans. 相似文献
67.
James A. McLean Kenneth P. Mathews William R. Solomon Peter R. Brayton Arthur A. Ciarkowski 《The Journal of allergy and clinical immunology》1977,59(2):165-170
Serial nasal, intracutaneous, or bronchial challenges were carried out with solutions containing 2- or 3-fold increments in histamine (H) or methacholine (Meth) concentration until nasal airway resistance (NAR) increased by more than 100%, a large intracutaneous reaction was elicited, or FEV1 decreased by 20% or more. Thirty nonatopic and 48 asymptomatic atopic subjects were studied, the latter group divided into rhinitic patients with and without asthma. Several types of data analysis demonstrated there was no significant difference in the nasal or cutaneous effects of H or Meth between the atopic and nonatopic groups. Comparable results were obtained in a subgroup of 39 subjects (13 normal, 13 atopic, and 13 atopic with asthma) who underwent all six test sequences (i.e., nasal, cutaneous, and bronchial with both drugs). As expected, the asthmatics showed significantly increased bronchial reactivity to both agents. In comparison with Meth, H had a much greater effect on the nasal mucosa and skin than on the bronchi. It is concluded that, contrary to bronchial responses, but in accord with cutaneous reactivity, the nasal responses of nonatopic subjects, atopic persons with allergic rhinitis alone, and subjects with both allergic rhinitis and asthma show no intergroup differences on testing with H or Meth. 相似文献
68.
Reibman J Hsu Y Chen LC Kumar A Su WC Choy W Talbot A Gordon T 《American journal of respiratory cell and molecular biology》2002,27(4):455-462
Environmental pollutants, including ambient particulate matter (PM), increase respiratory morbidity. Studies of model PM particles, including residual oil fly ash and freshly generated diesel exhaust particles, have demonstrated that PM affects inflammatory airway responses. Neither of these particles completely represents ambient PM, and therefore questions remain about ambient particulates. We hypothesized that ambient PM of different size fractions collected from an urban environment (New York City air), would activate primary culture human bronchial epithelial cells (HBECs). Because of the importance of granulocyte-macrophage colony-stimulating factor (GM-CSF) on inflammatory and immunomodulatory processes, we focused our studies on this cytokine. We demonstrated that the smallest size fraction (ultrafine/fine; < 0.18 micro m) of ambient PM (11 micro g/cm(2)), upregulated GM-CSF production (2-fold increase). The absence of effect of carbon particles of similar size, and the day-to-day variation in response, suggested that the chemical composition, but not the particle itself, was necessary for GM-CSF induction. Activation of the extracellular signal-regulated kinase and the p38 mitogen-activated protein kinase was associated with, and necessary for, GM-CSF release. These studies serve to corroborate and extend those on model particles. Moreover, they emphasize the role of the smallest size ambient particles in airway epithelial cell responses. 相似文献
69.
The authors examined the role of the ventral tegmental area (VTA) and nucleus accumbens (NAc) in the expression of ethanol-induced conditioned place preference (CPP). After cannulas were implanted, male DBA/2J mice underwent an unbiased Pavlovian-conditioning procedure for ethanol-induced CPP. Before preference testing, the mice were injected intra-VTA (Experiments 1 and 3) or intra-NAc (Experiment 2) with the nonselective opioid antagonist methylnaloxonium (0-ng, 375-ng, or 750-ng total infusion; Experiments 1 and 2) or the gamma aminobutyric acid (GABA(B)) agonist baclofen (0-ng, 25-ng, or 50-ng total infusion; Experiment 3). Intra-VTA methylnaloxonium or baclofen decreased ethanol-induced CPP, whereas intra-NAc methylnaloxonium had no effect. These findings indicate that the conditioned rewarding effect of ethanol is expressed through a VTA-dependent mechanism that involves both opioid and GABA(B) receptors. 相似文献
70.
H C Smith-Vaughan K S Sriprakash J D Mathews D J Kemp 《Journal of clinical microbiology》1995,33(5):1192-1195
PCR-ribotyping, a new typing method based on long PCR, has been developed for nontypeable Haemophilus influenzae (NTHi). Ribosomal operons of NTHi were amplified by long PCR and were found to be highly polymorphic for internal HaeIII sites. The technique was applied to 49 isolates previously subjected to conventional ribotyping, and the two methods showed a high level of concordance for serial isolates from individual subjects. PCR-ribotyping provides a powerful new typing tool for strain characterization in epidemiological investigations of NTHi. 相似文献