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   188975篇
  免费   1563篇
  国内免费   101篇
耳鼻咽喉   1268篇
儿科学   6888篇
妇产科学   3143篇
基础医学   18392篇
口腔科学   1739篇
临床医学   13688篇
内科学   34193篇
皮肤病学   978篇
神经病学   18092篇
特种医学   9787篇
外科学   30848篇
综合类   2378篇
一般理论   7篇
预防医学   18597篇
眼科学   2939篇
药学   10099篇
中国医学   630篇
肿瘤学   16973篇
  2024年   37篇
  2023年   150篇
  2022年   181篇
  2021年   412篇
  2020年   262篇
  2019年   336篇
  2018年   22240篇
  2017年   17582篇
  2016年   19811篇
  2015年   1255篇
  2014年   1307篇
  2013年   1470篇
  2012年   8052篇
  2011年   22014篇
  2010年   19442篇
  2009年   12100篇
  2008年   20408篇
  2007年   22576篇
  2006年   1458篇
  2005年   3072篇
  2004年   4171篇
  2003年   5038篇
  2002年   3120篇
  2001年   407篇
  2000年   510篇
  1999年   292篇
  1998年   342篇
  1997年   324篇
  1996年   160篇
  1995年   170篇
  1994年   147篇
  1993年   100篇
  1992年   84篇
  1991年   121篇
  1990年   170篇
  1989年   110篇
  1988年   74篇
  1987年   66篇
  1986年   47篇
  1985年   48篇
  1984年   44篇
  1983年   42篇
  1982年   46篇
  1980年   54篇
  1974年   39篇
  1968年   28篇
  1938年   64篇
  1934年   34篇
  1932年   62篇
  1930年   60篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
31.
Miroestrol and deoxymiroestrol are the most potent phytoestrogens of Pueraria candollei var. mirifica, having been proved as an effective herb for menopausal symptoms in folk medicines and clinical trials. To ensure efficacy and safety of P. candollei var. mirifica involved in nutraceutical products being available worldwide, the content of potent phytoestrogens as active ingredients should be specified. Therefore, in this study, we produced a monoclonal antibody for total analysis of potent estrogenic miroestrol and deoxymiroestrol, for which an analytical method was developed using a procedure for an indirect competitive enzyme-linked immunosorbent assay. The antibody exhibited equal reactivity against miroestrol and deoxymiroestrol. The sensitivity of determination was in the range of 31.3–500 ng/ml with high precision. The analytical parameters, such as accuracy (99.6–106% recovery) and high correlation with a HPLC–UV method, indicated the reliability of analysis. This method is of high performance, and it is cheap to control optimal miroestrol and deoxymiroestrol doses of P. candollei var. mirifica nutraceutical products.  相似文献   
32.
Lignans are widely distributed in plants and exhibit significant pharmacological effects, including anti-tumor and antioxidative activities. Here, we describe the total synthesis of schizandriside (1), a compound we previously isolated from Saraca asoca by monitoring antioxidative activity using the 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay. Starting from a tandem Michael-aldol reaction, the lignan skeleton was synthesized in 6 steps, including a cyclization step. To determine the stereochemistry of 1, we synthesized the natural product (±)-isolariciresinol (18) from alcohol 17. Comparison of the spectral data showed good agreement. Glycosylation was investigated using four different glycosyl donors. Only the Koenigs–Knorr condition using silver trifluoromethanesulfonate with 1,1,3,3-tetramethylurea provided the glycosylated product. Deprotection and purification using reverse-phase high-performance liquid chromatography gave schizandriside (1) and its diastereomer saracoside (2). Synthesized 1, 2 and 18 showed antioxidant activity with IC50?=?34.4, 28.8, 53.0 μM, respectively.  相似文献   
33.
Pachymic acid (PA) is a lanostane type triterpenoid isolated from Poria cocos, which possesses an anti-tumor effect in breast cancer, prostate cancer, lung cancer, and bladder cancer cells. In this study, we investigated the effect of PA on the growth and apoptosis of human immortalized cell line (HOS) and primary osteosarcoma cells by a Cell Counting Kit-8 (CCK-8) and Annexin V and propidium iodide (PI) staining, respectively. Western blot was used to measure the expression of cleaved Caspase 3, PTEN, and AKT, as well as the AKT phosphorylation. The Caspase 3 activity was determined using the Caspase-3 Colorimetric Assay Kit. From the results, PA significantly reduced cell proliferation in a concentration- and time-dependent manner. PA also induced cell apoptosis in a dose-dependent fashion. PA treatment led to increased Caspase 3 activation and PTEN expression, as well as reduced AKT phosphorylation. Moreover, Ac-DEVD-CHO (a Caspase 3/7 inhibitor) pre-treatment or PTEN knockdown partially blocked the effects of PA on cell proliferation and apoptosis. Caspase 3/7 inhibitor had an additive effect with PTEN knockdown. Collectively, our results suggested that induction of apoptosis by PA was mediated in part by PTEN/AKT signaling and Caspase 3/7 activity. This study provides evidence that PA might be useful in the treatment of human osteosarcoma.  相似文献   
34.
Two new secoiridoid glucosides, ilexpublignoside (1), pubzenoside (2), and a new lignan, ilexlignan B (3), along with seven known compounds (4–10) were isolated from the roots of Ilex pubescens for the first time. Their chemical structures were elucidated on the basis of extensive spectroscopic methods, including IR, UV, HR-ESI–MS, CD, NMR experiments, as well as comparison with the reported data.  相似文献   
35.
36.
37.
38.
39.
40.
The purpose of this study is to develop a novel breast abnormality detection system by utilizing the potential of infrared breast thermography (IBT) in early breast abnormality detection. Since the temperature distributions are different in normal and abnormal thermograms and hot thermal patches are visible in abnormal thermograms, the abnormal thermograms possess more complex information than the normal thermograms. Here, the proposed method exploits the presence of hot thermal patches and vascular changes by using the power law transformation for pre-processing and singular value decomposition to characterize the thermal patches. The extracted singular values are found to be statistically significant (p?<?0.001) in breast abnormality detection. The discriminability of the singular values is evaluated by using seven different classifiers incorporating tenfold cross-validations, where the thermograms of the Department of Biotechnology-Tripura University-Jadavpur University (DBT-TU-JU) and Database of Mastology Research (DMR) databases are used. In DMR database, the highest classification accuracy of 98.00% with the area under the ROC curve (AUC) of 0.9862 is achieved with the support vector machine using polynomial kernel. The same for the DBT-TU-JU database is 92.50% with AUC of 0.9680 using the same classifier. The comparison of the proposed method with the other reported methods concludes that the proposed method outperforms the other existing methods as well as other traditional feature sets used in IBT based breast abnormality detection. Moreover, by using Rank1 and Rank2 singular values, a breast abnormality grading (BAG) index has also been developed for grading the thermograms based on their degree of abnormality.  相似文献   
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