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   1624篇
  免费   118篇
  国内免费   4篇
  2024年   5篇
  2023年   21篇
  2022年   69篇
  2021年   91篇
  2020年   55篇
  2019年   93篇
  2018年   110篇
  2017年   61篇
  2016年   77篇
  2015年   71篇
  2014年   73篇
  2013年   137篇
  2012年   104篇
  2011年   106篇
  2010年   68篇
  2009年   53篇
  2008年   61篇
  2007年   60篇
  2006年   45篇
  2005年   50篇
  2004年   54篇
  2003年   43篇
  2002年   34篇
  2001年   12篇
  2000年   12篇
  1999年   8篇
  1998年   6篇
  1996年   13篇
  1994年   5篇
  1992年   8篇
  1990年   10篇
  1989年   3篇
  1988年   7篇
  1987年   8篇
  1986年   7篇
  1985年   9篇
  1984年   8篇
  1983年   6篇
  1982年   3篇
  1981年   7篇
  1980年   7篇
  1979年   6篇
  1978年   6篇
  1977年   8篇
  1976年   4篇
  1974年   4篇
  1973年   5篇
  1971年   3篇
  1970年   3篇
  1969年   4篇
排序方式: 共有1746条查询结果,搜索用时 296 毫秒
991.
992.
Plant Molecular Biology - We reported the functional characterization of cDNAs encoding short-chain isoprenyl diphosphate synthases that control the partitioning of precursors for lavender...  相似文献   
993.
994.
The role of ovarian hormones, nitric oxide, and their interaction on learning and memory has been widely investigated. The objective of present study was to investigate different effects of chronic administration of inducible nitric oxide synthase inhibitor, aminoguanidine (AM) on learning and memory of ovariectomized (OVX) and na?ve (Sham) female rats. Thirty-two rats were divided into four groups: 1) Sham, 2) OVX, 3) Sham-AM and 4) OVX-AM. The animals of Sham-AM and OVX-AM chronically received 100 mg/kg/day of aminoguanidine during 8 weeks before 5 test days. The animals in Sham and OVX groups received 1 ml/kg saline instead of aminoguanidine. The animals were tested in Morris water maze and the escape latency and traveled path to reach the platform were compared between groups. On the fifth day, the platform was removed, and the animals were allowed to swim for 60 s ( prob trial). The time spent in the target quadrant (Q1) was compared between groups.Results showed that the escape latency and traveled path in OVX group were significantly higher than in the Sham group (p<0.01). Both escape latency and traveled path in the Sham-AM group was significantly higher than in the Sham group (p<0.01) however, there was no significant difference between OVX-AM and OVX groups.The time spent by the animals of OVX group in the target quadrant (Q1) during the probe trial was significantly lower than that in the Sham group (p<0.01). The animals of the Sham-AM group spent shorter times in the target quadrant in comparison with the Sham group (p<0.01). There was no significant difference between the OVX and OVX-AM groups in the time spent in tarthe get quadrant. It is concluded that the effect of aminoguanidine on learning and memory is different in the presence or absence of ovarian hormones but it needs further investigation.  相似文献   
995.
AimsWe recently reported that acute exposure to nicotine vasodilates the renal vasculature of male rats via facilitation of endothelial nitric oxide synthase (eNOS). In this study, we investigated whether this effect of nicotine is sexually dimorphic and the role of estrogen in modulating the nicotine effect.Main methodsNicotine-evoked vasodilation was evaluated in phenylephrine-preconstricted perfused kidneys obtained from male, proestrus female, ovariectomized (OVX) and estrogen-replaced OVX (OVXE2) rats.Key findingsNicotine infusion (5 × 10? 5, 1 × 10? 4, and 5 × 10? 4 M) produced greater concentration-dependent reductions in the renal perfusion pressure (RPP) in an isolated kidney from proestrus females than from males. Inhibition of NOS by NG-nitro-l-arginine abolished the nicotine-evoked reduction in RPP and abolished the gender difference in the nicotine effect. Nicotine vasodilation was also attenuated in kidneys isolated from OVX and diestrus rats, models characterized by reduced estrogen levels. Further, estrogen or l-arginine supplementation in OVX rats largely restored the renal vasodilatory response to nicotine. Estrogen receptor blockade by tamoxifen abrogated the enhanced nicotine-evoked vasodilation elicited by E2 in OVX rats. The nitrite/nitrate levels and protein expressions of eNOS and α7 nicotinic cholinergic receptor (α7 nAChRs) were significantly higher in renal tissues of OVXE2 compared with OVX rats, suggesting a facilitatory effect for E2 on α7 nAChRs/eNOS signaling.SignificanceEstrogen-dependent facilitation of NOS signaling mediates the enhanced vasodilator capacity of nicotine in the renal vasculature of female rats. Preliminary evidence also suggests a potential role for α7 nAChRs in this estrogen-dependent phenomenon.  相似文献   
996.
Cellular replacement therapy is a potential therapeutic strategy for diabetes. In this study, we investigated the effect of transplantation of induced mouse embryonic stem cells (mESCs) into endoderm and early hepatocyte-like cells in streptozotocin (STZ)-diabetic mice. After embryoid body (EB) formation from mESC, the EBs were cultured in the presence of dexamethasone (DEX) and insulin for 4 days then was added acidic fibroblast growth factor (aFGF), hepatocyte growth factor (HGF) and oncostatin M (OSM) for 10 days, respectively. Blood glucose levels, intraperitoneal glucose tolerance (IGT) test and islet histology were assessed. The result revealed that transplantation of induced mESCs into early hepatocyte-like cells could repair pancreatic islets of control group. Blood glucose levels and intraperitoneal glucose tolerance test were significantly improved in test group compared to control group. Furthermore, there was significant increase in the number of islets in test group compared to control group. The findings declare that induced mESCs into endoderm and early hepatocyte-like cells, are appropriate candidate for regenerative therapy of pancreatic islets in type I diabetes.  相似文献   
997.
Repair and biochemical effects of DNA-protein crosslinks   总被引:1,自引:0,他引:1  
  相似文献   
998.
A 1-year study found seven infectious human adenovirus serotypes, including Ad3, Ad31, Ad46, Ad27, Ad22, Ad51, and clinical clone PB3, in wastewaters of two major cities in Canada. Comparative genomic analysis revealed the existence of the reportedly highly contagious Ad3a16/18 genotypes. This is the first report of Ad3a16/18 genotypes in North America.  相似文献   
999.
The increasing utilization of synthetic (encapsulated) seeds for germplasm conservation and propagation necessitates the assessment of genetic stability of conserved propagules following their plantlet conversion. We have assessed the genetic stability of synthetic seeds of Cannabis sativa L. during in vitro multiplication and storage for 6 months at different growth conditions using inter simple sequence repeat (ISSR) DNA fingerprinting. Molecular analysis of randomly selected plants from each batch was conducted using 14 ISSR markers. Of the 14 primers tested, nine produced 40 distinct and reproducible bands. All the ISSR profiles from in vitro stored plants were monomorphic and comparable to the mother plant which confirms the genetic stability among the clones. GC analysis of six major cannabinoids [Δ9-tetrahydrocannabinol, tetrahydrocannabivarin, cannabidiol, cannabichromene, cannabigerol and cannabinol] showed homogeneity in the re-grown clones and the mother plant with insignificant differences in cannabinoids content, thereby confirming the stability of plants derived from synthetic seeds following 6 months storage.  相似文献   
1000.
This study has been made to determine the potential genotoxicity of Schistosoma mansoni on lymphocytes of infected patients using different mutagenic end points. The protective role of antioxidants pro vitamin β-carotene and vitamin E in minimizing these genotoxic effect was also studied. The study focused on the effect of schistosomiasis on the induction of sister chromatid exchange (SCEs) and other chromosomal aberrations. This work was conducted on 24 Schistosoma mansoni infected patients and 10 healthy adults as a control group. Lymphocytes from peripheral blood of patients and control group were used for culture and subsequent cytogenetic studies. The results indicated that schistosomiasis was genotoxic in all examined tests. It induced a significant increase in the percentage of structural chromosomal aberrations and the frequency of SCEs. It also inhibited cell division and caused cell cycle delay. Lymphocyte cultures of S. mansoni patients treated with 10 μg/ml β-carotene or 20 mg/ml vitamin E showed a significant decrease in the percentage of structural chromosomal aberrations and the frequency of SCEs. Schistosomiasis has a genotoxic effect on peripheral blood lymphocytes. The use of the antioxidants β-carotene and vitamin E can be considered a promising approach not only toward inhibiting the genetic damage of schistosomiasis but also as prophylactic agents against infection with S mansoni. Furthermore, higher doses of antioxidant drugs, β-carotene and vitamin E, should be tried as an adjuvants to conventional therapy in a trial to improve treatment of schistosomiasis.  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