首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   3686篇
  免费   189篇
  国内免费   45篇
耳鼻咽喉   81篇
儿科学   150篇
妇产科学   178篇
基础医学   358篇
口腔科学   95篇
临床医学   261篇
内科学   732篇
皮肤病学   77篇
神经病学   238篇
特种医学   190篇
外科学   701篇
综合类   125篇
预防医学   283篇
眼科学   73篇
药学   166篇
中国医学   29篇
肿瘤学   183篇
  2024年   4篇
  2023年   30篇
  2022年   41篇
  2021年   114篇
  2020年   72篇
  2019年   69篇
  2018年   154篇
  2017年   115篇
  2016年   138篇
  2015年   218篇
  2014年   238篇
  2013年   239篇
  2012年   419篇
  2011年   322篇
  2010年   116篇
  2009年   191篇
  2008年   89篇
  2007年   184篇
  2006年   112篇
  2005年   220篇
  2004年   283篇
  2003年   168篇
  2002年   73篇
  2001年   17篇
  2000年   12篇
  1999年   19篇
  1998年   39篇
  1997年   52篇
  1996年   6篇
  1995年   4篇
  1994年   3篇
  1993年   8篇
  1992年   4篇
  1991年   6篇
  1990年   9篇
  1989年   19篇
  1988年   14篇
  1987年   11篇
  1986年   13篇
  1985年   7篇
  1984年   8篇
  1983年   13篇
  1982年   10篇
  1981年   7篇
  1980年   3篇
  1979年   6篇
  1978年   5篇
  1977年   3篇
  1965年   2篇
  1964年   2篇
排序方式: 共有3920条查询结果,搜索用时 15 毫秒
21.
The riv method:     
  相似文献   
22.
23.
Matrix metalloproteinases (MMPs) are zinc dependent endopeptidases implicated in cancer invasion and metastasis. Gelatin zymography was performed on 84 human breast carcinomas and seven normal breast tissues. The precursor form of MMP-2 (72 kDa) was found in 11 (12%) samples, while its two activated forms, i.e. 62 kDa and 59 kDa, were found in three (6%) and 34 (40%) samples respectively. In contrast to MMP-2, most of the samples (52%) contained MMP-9 in its precursor form. Using ELISA, MMP-1 levels were found in 12% of the samples while MMP-3 levels were found in only 2% of the samples. Levels of MMP-2, -3 and -9 correlated inversely with numbers of nodal metastases. Neither MMP-2 nor -9 levels were significantly related to patient outcome. However, patients with high levels of a 50-kDa gelatinase band after zymography had a significantly better survival than patients with low levels. This species was never observed in normal breast tissue.  相似文献   
24.
We examined the localization of basic fibroblast growth factor (bFGF) in a series of human breast carcinomas using immunohistochemistry. Staining was observed in tumour cells in 15 out of 54 (28%) tumours and in the adjacent stroma in 34 out of 54 (63%) tumours examined. No correlation was observed between positive staining of these two compartments. The relationship between bFGF staining and expression of the metalloprotease stromelysin-3, and between bFGF and microvessel density, was examined. A statistically significant correlation (P < 0.003) was observed between bFGF staining of the stromal compartment and high expression of stromelysin-3 (ST-3; MMP-11) metalloprotease mRNA by stromal cells. In contrast, no correlation was observed between bFGF and intratumour microvessel density (IMD). These results raise the possibility that bFGF may be involved in the induction of stromelysin-3 mRNA expression in breast cancer stroma.  相似文献   
25.
Inherited susceptibility to ovarian cancer has been associated with germline defects at several loci. The major known ovarian cancer susceptibility gene is BRCA1 on chromosome 17q, which confers a risk of approximately 60% by the age of 70 years. Truncating mutations in BRCA2 on chromosome 13q also predispose to ovarian cancer, although they confer a lower risk than mutations in BRCA1. We have studied the molecular basis of ovarian cancer predisposition in a Finnish family with three affected sisters. Analysis of polymorphic markers provided evidence against linkage to BRCA1, but the sibship was consistent with linkage to BRCA2. Conformation-sensitive gel electrophoresis was used to screen the entire coding sequence of BRCA2. A G to A transition at nucleotide 8702 was observed, which is predicted to convert glycine 2901 to aspartate in the encoded protein. This sequence variant was not detected in 220 cancer-free Finnish control individuals, or in several hundred cancer families of many nationalities previously screened for BRCA2 mutations. Taken together with the fact that this amino acid residue and the surrounding region of BRCA2 is identical in mouse and chicken, the data suggest that this alteration is a disease-causing BRCA2 missense mutation. Previously published data indicate that the risks of breast and ovarian cancer conferred by BRCA2-truncating mutations varies with the position of the mutation in the gene. The missense mutation reported here suggests that the BRCA2 domain including and surrounding glycine 2901 may be more important in preventing neoplastic transformation in ovarian epithelium than in breast epithelium.  相似文献   
26.
Urokinase-type plasminogen activator (uPA) is a potentially important prognostic factor in breast cancer for identifying patients at high risk of recurrence. This retrospective study assessed two enzyme-linked immunosorbent assay (ELISA) methods measuring uPA antigen levels in 499 primary breast cancer cytosols. Both uPA methods were applied to cytosols used routinely for oestrogen (ER) and progesterone (PgR) receptor assays. uPA was determined using a classical ELISA method (Imubind; American Diagnostica) and a novel automatic immunoluminometric assay (Lia; Sangtec Medical). The uPA Imubind method revealed about twice as much uPA antigen (median 0.75 ng mg(-1) protein) as the uPA Lia method (median 0.38 ng mg(-1) protein). The correlation coefficient between the two methods was acceptable (r = 0.81), but the two techniques are not interchangeable. Univariate analyses confirmed the poor outcome of patients whose tumours contained large amounts of uPA, regardless of the technique used. Multivariate analyses showed that uPA Imubind and uPA Lia values were both strong independent prognostic factors.  相似文献   
27.
Purpose: The aim of the study was to investigate whether maternal serum TSP-1 level was associated with PE.

Materials and methods: In our case control study, 84 pregnant women in the third trimester were included. Forty-one of them were healthy and 43 of them were with the diagnosis of PE. The diagnosis was based on the definitions of the National High Blood Pressure Education Program working Group on High Blood Pressure in Pregnancy. Preeclamptic patients were divided into two subgroups as mild and severe. Blood pressure (BP) of pregnant women were obtained in left-side lying position using a mercury sphygmomanometer after at least 10 minutes of rest. Ten milliliters of venous blood was taken from every pregnant women and dispensed into lithium heparin and serum was obtained. Samples were stored at ?80?°C until analyzed. Serum TSP-1 level was measured using enzyme-linked immunosorbent assay (ELISA). All tests were two-tailed and p < .05 was considered to be statistically significant.

Results: TSP-1 level was significantly lower in PE group than in controls (p?=?.003). Platelet counts were similar in two groups (p = .26). TSP-1 levels were significantly lower in severe PE than in mild PE cases. According to the subgroup analysis, TSP-1 level was found significantly lower in severe preeclampsia group compared to control group (p = .015).

Conclusions: In light of the association between endothelial dysfunction and preeclampsia, we claim that lower levels of TSP-1 which is released mostly from endothelial cells seem to reflect disease severity in PE. Our study reveals that maternal serum TSP-1 levels decrease in pregnant women presenting with PE and TSP-1 may be a new biomarker for the detection of PE and even severity of it. Further studies especially prospective ones with greater numbers of cases are needed.  相似文献   
28.
29.
Sixteen polymorphic microsatellite loci are described for Spergularia echinosperma, an endangered plant endemic to Central Europe. Based on 51 individuals, the number of alleles per locus ranged from 2 to 5, and the observed and expected heterozygosities were both 0.00–0.17. The markers can be valuable tool to conservation genetics of this species across its distributional range.  相似文献   
30.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号