全文获取类型
收费全文 | 6774篇 |
免费 | 633篇 |
国内免费 | 748篇 |
专业分类
8155篇 |
出版年
2024年 | 25篇 |
2023年 | 110篇 |
2022年 | 271篇 |
2021年 | 391篇 |
2020年 | 308篇 |
2019年 | 380篇 |
2018年 | 315篇 |
2017年 | 244篇 |
2016年 | 319篇 |
2015年 | 445篇 |
2014年 | 487篇 |
2013年 | 506篇 |
2012年 | 654篇 |
2011年 | 551篇 |
2010年 | 335篇 |
2009年 | 293篇 |
2008年 | 328篇 |
2007年 | 293篇 |
2006年 | 231篇 |
2005年 | 228篇 |
2004年 | 187篇 |
2003年 | 185篇 |
2002年 | 152篇 |
2001年 | 134篇 |
2000年 | 108篇 |
1999年 | 90篇 |
1998年 | 59篇 |
1997年 | 58篇 |
1996年 | 59篇 |
1995年 | 48篇 |
1994年 | 39篇 |
1993年 | 32篇 |
1992年 | 37篇 |
1991年 | 26篇 |
1990年 | 31篇 |
1989年 | 19篇 |
1988年 | 18篇 |
1987年 | 20篇 |
1986年 | 8篇 |
1985年 | 12篇 |
1984年 | 8篇 |
1983年 | 15篇 |
1982年 | 6篇 |
1977年 | 6篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1972年 | 11篇 |
1971年 | 9篇 |
1970年 | 7篇 |
1968年 | 8篇 |
排序方式: 共有8155条查询结果,搜索用时 15 毫秒
91.
本文报道了6个中国被子植物新记录种及1个新记录亚种, 分别是采自西藏的灰滨藜(Atriplex pallida)、类球花藜(Blitum litwinowii)、滨藜状藜(Chenopodium atripliciforme)、土耳其针茅(Stipa turkestanica)、扁果岩蓼(Polygonum cognatum subsp. chitralicum)及新疆的宝格达黄芪(Astragalus baitagensis)和神香草叶千屈菜(Lythrum hyssopifolia), 观察了部分类群的微形态特征并提供了生境或形态图。凭证标本均存放于内蒙古大学植物标本馆(HIMC)。 相似文献
92.
Gao X. Zhang Y. Mu J. Q. Chen K. X. Zhang H. F. Bi K. S. 《Russian Journal of Bioorganic Chemistry》2021,47(2):420-431
Russian Journal of Bioorganic Chemistry - Guan-Xin-Shu-Tong capsule is a widely used traditional Chinese medicine for the treatment of cardiovascular diseases. However, little knowledge about the... 相似文献
93.
Xiao Yang Ya-ping Wang Feng-xiang Liu Ke Zeng Ming-quan Qian Gang Chen Lei Shi Guo-xing Zhu 《In vitro cellular & developmental biology. Animal》2013,49(4):270-278
To evaluate the different traits of mesenchymal stem cell (MSC) isolated from osteosarcoma (OS) and normal bone marrow (BM) induced by bone-morphogenetic protein-2 (BMP-2). MSCs from implanted osteosarcoma or femur bone marrow were isolated and cultured. Differentiation potency was verified and phenotypes were evaluated by flow cytometry. Increased or decreased expressions of BMP-2 were delivered by adenovirus and lentivirus vector, respectively. Expressions of VEGF, EMMPRIN, and MMP-9 were examined. Cell cycle, apoptosis, invasiveness, and proliferation assays were performed between the transfected groups and controls. Increased BMP-2 induced over-expression of VEGF, EMMPRIN, and MMP-9 in OS- and BM-MSCs both intra- and extra-cellularly. Decreased BMP-2 expression induced inhibition of the factors. Increased BMP-2 also induced less population of cells at G1 phase, more apoptotic cells, more cells that invade through Transwell membrane, and faster proliferation in OSMSC compared to those in BMMSC. BMP-2 induced higher expression of tumorigenic factors, which could be responsible for promoting the proliferation and aggressiveness of OSMSC over BMMSC. 相似文献
94.
95.
Meina Wang Erik R Sampson Hongting Jin Jia Li Qiao H Ke Hee-Jeong Im Di Chen 《Arthritis research & therapy》2013,15(1):R5
Introduction
Osteoarthritis (OA) is a degenerative joint disease affecting a large population of people. The mechanism of this highly prevalent disease is not fully understood. Currently there is no effective disease-modifying treatment for OA. The purpose of this study was two-fold: 1) to investigate the role of MMP13 in the development of OA; and 2) to evaluate the efficacy of the MMP13 inhibitor CL82198 as a pharmacologic treatment for preventing OA progression.Methods
To investigate the role of the endogenous Mmp13 gene in OA development, tamoxifen was administered to two-week-old Col2CreER;Mmp13fx/fx (Mmp13Col2ER) and Cre-negative control mice for five days. OA was induced by meniscal-ligamentous injury (MLI) when the mice were 10 weeks old and MLI or sham-operated joints were harvested 4, 8, 12, or 16 weeks after surgery. To evaluate the efficacy of CL82198, MLI surgery was performed on 10-week-old wild type mice. CL82198 or saline was administered to the mice daily beginning immediately after the surgery for up to 16 weeks. The joint tissues collected from both experiments were evaluated by cartilage grading, histology/histomorphometry, immunohistochemistry (IHC), and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining. The ability of CL82198 to inhibit MMP13 activity in vitro was confirmed by ELISA.Results
The OA progression was decelerated in Mmp13Col2ER mice 8, 12, and 16 weeks post-surgery. Cartilage grading by blinded observers confirmed decreased articular cartilage degeneration in Mmp13Col2ER mice at 8, 12 and 16 weeks compared to Cre-negative mice. Histomorphometric analysis demonstrated that Mmp13Col2ER mice had a higher articular cartilage area and thickness at 12 and 16 weeks post-surgery compared to the control mice. Results of IHC revealed greater type II collagen and proteoglycan expression in Mmp13Col2ER mice. Chondrocyte apoptosis, as determined by TUNEL staining, was higher in control mice compared to Mmp13Col2ER mice. CL82198 inhibited MMP13 activity in conditioned media from vehicle (> 85%) or bone morphogenetic protein 2 (BMP2)-treated (> 90%) primary murine sternal chondrocytes. Intraperitoneal injection of CL82198 decelerated MLI-induced OA progression, increased type II collagen and proteoglycan levels, and inhibited chondrocyte apoptosis compared to saline treatment as determined by OA grading, histology, histomorphometry, IHC, and TUNEL staining, respectively.Conclusions
Mmp13 is critical for OA progression and pharmacologic inhibition of MMP13 is an effective strategy to decelerate articular cartilage loss in a murine model of injury-induced knee OA. 相似文献96.
97.
98.
Guangxia Cui Huijie Leng Ke Wang Jianwei Wang Sainan Zhu Jing Jia Xing Chen Weiguang Zhang Lihua Qin Wenpei Bai 《PloS one》2013,8(12)
This study aims to evaluate the effects of Remifemin (isopropanolic extract of Cimicifuga Racemosa) on postmenopausal osteoporosis. 120 female Sprague-Dawley rats were randomly assigned to four groups: sham surgery with vehicle, ovariectomy with vehicle, ovariectomy with estradiol valerate, or ovariectomy with Remifemin. Daily oral administrations of the vehicle, estradiol valerate, or Remifemin began 2 weeks after surgery and lasted to 4, 8, or 12 weeks. Ten rats in each group were sacrificed at each timestep with assessment of bone mineral density, trabecular bone structure, and biomechanical parameters of the femur and lumbar vertebra. Bone turnover markers were evaluated 12 weeks after surgery. Both drugs prevented bone density loss in the distal end of the femur and preserved the trabecular bone structure in both the lumbar vertebra and distal end of the femur following ovariectomy. Both drugs protected bone stiffness at the tested regions and reduced bone reabsorption in ovariectomized rats. The preventive effects of Remifemin against bone-loss can rival those of estradiol valerate if treatment duration is adequately extended. In conclusion, Remifemin may demonstrate equivalent effects to estradiol valerate in terms of preventing postmenopausal osteoporosis. 相似文献
99.
Six new triterpenoids, meliasenins S–X ( 1 – 6 , resp.), were isolated from the stem bark of Melia toosendan. Their structures were elucidated by mass spectrometry, NMR experiments, and comparison with the known compounds. Particularly, the absolute configuration at C(24) in new compounds was determined through their CD spectra of the [Pr(FOD)3] complex (fod=1,1,1,2,2,3,3,7,7,7‐decafluoroheptane‐4,6‐dione) in CCl4, as well as by using Mosher's method. 相似文献
100.