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   636篇
  免费   39篇
  国内免费   1篇
  2023年   2篇
  2022年   3篇
  2021年   19篇
  2020年   9篇
  2019年   9篇
  2018年   21篇
  2017年   13篇
  2016年   22篇
  2015年   17篇
  2014年   28篇
  2013年   49篇
  2012年   61篇
  2011年   46篇
  2010年   33篇
  2009年   29篇
  2008年   36篇
  2007年   45篇
  2006年   34篇
  2005年   29篇
  2004年   36篇
  2003年   25篇
  2002年   21篇
  2001年   3篇
  2000年   3篇
  1999年   4篇
  1998年   5篇
  1997年   6篇
  1996年   8篇
  1995年   4篇
  1994年   6篇
  1993年   5篇
  1992年   3篇
  1991年   5篇
  1990年   5篇
  1989年   2篇
  1988年   2篇
  1987年   1篇
  1986年   6篇
  1985年   3篇
  1984年   3篇
  1983年   4篇
  1982年   2篇
  1981年   2篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
  1966年   2篇
排序方式: 共有676条查询结果,搜索用时 31 毫秒
611.
OBJECTIVE: To measure mean nuclear volume (MNV), estimated by the stereologic intercept method, in ovarian serous carcinomas and to compare that between omentum-positive cases (cases with omental metastasis) and -negative cases. STUDY DESIGN: This retrospective study consisted of 29 cases (stage I and II = 13 cases, and stage IIIb = 16 cases) of ovarian papillary serous cystadenocarcinoma. MNV of all cases (at primary and metastatic sites) was estimated with an image cytometer. The nuclear point intersection method was used to measure nuclear volume. Mean intercepted diameters of at least 50 nuclei were measured. MNV was correlated with histologic grade, International Federation of Gynecology and Obstetrics (FIGO) staging of ovarian malignancy and primary tumor versus metastatic deposits. RESULTS: MNVs estimated in omentum-negative (FIGO stage I and II) and omentum-positive (FIGO stage IIIb) cases were 1,022.48 +/- 608.45 and 2,152 +/- 1,317.51 microns 3 (P = .05, Student t test), respectively. Significant differences in MNV were also observed among the different grades of tumor. However, no significant difference was observed between MNVs of primary and metastatic tumors in omentum-positive cases. CONCLUSION: Estimates of MNV on conventional histopathology sections may provide objective and useful criteria for relatively subjective histopathology grading and staging (FIGO stage I and II vs. IIIb).  相似文献   
612.
Total 5-HT binding sites and 5-HT1A receptor density was measured in brain regions of rats treated with imipramine (5 mg/kg body wt), desipramine (10 mg/kg body wt) and clomipramine (10 mg/kg body wt), for 40 days, using [3H]5-HT and [3H]8-OH-DPAT, respectively. It was observed that chronic exposure to tricyclic antidepressants (TCAs) results in significant downregulation of total [3H]5-HT binding sites in cortex (42–76%) and hippocampus (35–67%). The 5-HT1A receptor density was, however, decreased significantly (32–60%) only in cortex with all the three drugs. Interestingly, in hippocampus imipramine treatment increased the 5-HT1A receptor density (14%). The affinity of [3H]8-OH-DPAT was increased only with imipramine treatment both in cortex and hippocampus. The affinity of [3H]5-HT to 5-HT binding sites in cortex was increased with imipramine treatment and decreased with desipramine and clomipramine treatment. 5-HT sensitive adenylyl cyclase (AC) activity was significantly increased in cortex with imipramine (72%) and clomipramine (17%) treatment, whereas in hippocampus only imipramine treatment significantly increased AC activity (50%). In conclusion, chronic treatment with TCAs results in downregulation of cortical 5-HT1A receptors along with concomitant increase in 5-HT stimulated AC activity suggesting the involvement of cortical 5-HT1A receptors in the mechanism of action of TCAs.  相似文献   
613.
Barley stripe rust caused by Puccinia striiformis f.sp. hordei (PSH) is one of the major diseases in barley production regions worldwide. A total of 336 barley genotypes with diverse genetic backgrounds targeted for low‐input barley production were tested for seedling and adult‐plant stage resistance against six PSH races (0S0, 0S0‐1, 1S0, 4S0, 5S0 and 7S0) originated from India. The seedling resistance was evaluated by inoculating the barley genotypes with six races separately under controlled conditions in Shimla, India. The same barley genotypes were evaluated for adult‐plant stage resistance in the Agricultural Research Station (ARS) of Rajasthan Agriculture University, Durgapura, Rajasthan, India. Out of the 336 barley genotypes tested for seedling resistance, 119 (35.4%), 101 (30.1%), 87 (25.9%), 100 (29.8%), 91 (27.1%) and 70 (20.8%) genotypes were resistant to races 0S0, 0S0‐1, 1S0, 4S0, 5S0 and 7S0, respectively. In the field, 102 (30.3%) genotypes showed the resistance response of which 18 (5.3%) genotypes were highly resistant to PSH. Barley genotypes AM‐14, AM‐177, AM‐37, AM‐120, AM‐300, AM‐36, AM‐103, AM‐189, AM‐291, AM‐275 and AM‐274 showed resistance response to all six races at seedling and adult‐plant stages. Seedling resistance reported in the current study is effective against the newly emerged race 7S0 and previously reported five races in India. Therefore, resistant barley genotypes identified in the current study provided effective protection against all six races at seedling and adult‐plant stages. The stripe rust resistance identified in the current studies may be potential donors of stripe rust resistance to barley breeding programmes in India and elsewhere.  相似文献   
614.
In eastern and southern part of India Dregea volubilis (Family Asclepediaceae) is widely used as anthelmintic in traditional system of medicine. The present study was conducted to evaluate the fasciocidal activity of the methanol extract of D. volubilis leaves (MEDV) and to observe the drug’s effect on organisms through scanning electron microscopic (SEM) study. Live parasites (Trematode: Fasciola gigantica) were collected in 0.9% phosphate-buffered saline from the bile ducts of buffalo. Those were incubated in the said media at 37 ± 1 °C either as control, or with MEDV at 5, 10, 25, 50 and 100 mg/ml as test groups or with albendazole at 10 mg/ml as standard group. The efficacy of the extract was determined on the basis of paralysis (temporary loss of spontaneous movement of the organisms) and/or death of the liver flukes. Death was confirmed when the organisms lost their motility permanently and their motility could not be revived even when vigorously shaken or dipped in warm water. MEDV at all concentration effectively paralyzed first and then killed the liver flukes (p < 0.001). Maximum fasciocidal activity was found with concentration of 100 mg/ml at 38.83 ± 3.41 min. Through SEM study, severe damages were observed in both the suckers as well as on the tegumental surfaces of the treated liver flukes. The study confirmed the fasciocidal activity of the MEDV.  相似文献   
615.
616.
Genetic stability and phytochemical analysis of in vitro established plants of Picrorhiza kurroa Royle ex Benth, have been carried out. Random amplified polymorphic DNA (RAPD) and inter simple sequence repeats (ISSR) markers were used to assess the genetic fidelity of tissue culture products including three adventitious shoots from three calli and 6 months old tissue culture raised plants growing in green house condition with mother plant. Apparent genetic variation was detected in the five types of plant materials. The percentage of polymorphic bands in the RAPD and ISSR analysis were 16.25 and 14.54 %, respectively. The genetic similarity was calculated on the basis of RAPD and ISSR data among the five types of plant materials and were ranged from 0.5 to 1.0 (mean 0.75) and 0.47 to 1.0 (mean 0.73), respectively. The similarity coefficient by both RAPD and ISSR analysis revealed that differences between tissue culture raised plants and mother plant was not remarkable, but notable differences were observed among three adventitious shoots regenerated from three calli. The phytochemical analysis of tissue culture raised products showed higher secondary metabolite (picrotin and picrotoxinin) content as compare to mother plant. The information gained on genetic stability/variability will be valuable for the large scale propagation and secondary metabolite production of P. kurroa.  相似文献   
617.
The demand for petroleum and petroleum products is increasing day by day, while oil spills and improper discharge of industrial wastes contributes to the rising contamination of the environment with petroleum hydrocarbon. Petroleum hydrocarbon spills cause various carcinogenic and neurotoxic effects, and thus effective treatment strategies are required. The various physical and chemical methods currently in use are costly and leave toxic residues in the environment. In contrast, bioremediation is a promising technology in the treatment of petroleum hydrocarbon contamination because of its high effectiveness, lower cost and environmental synergy. Here, we review the biodegradation of petroleum hydrocarbon and various factors influencing this process.  相似文献   
618.
Abstract

Nuclear magnetic resonance structures of a nonapeptide, ERFKCPCPT, selected from the DNA binding domain of human polymerase-a, were determined by complete relaxation matrix analysis of transverse NOE data. The structures exhibit a type III turn with residues KCPC, and the remaining residues exhibit non-ordered structures. The turn was confirmed by α, N (i,i+3) connectivity, a low temperature coefficient of NH chemical shift (?3.1 × 1O?3) of the fourth residue, 3JNHα coupling constants, and characteristic CD peaks at 228 and 200 nm. Furthermore, ø and ψ dihedral angles for the i + 1, and i + 2 residues of the tum are found to be?80 and?41 and?60 and?40 degrees. The first proline residue is trans- while the second exists in both eis- and trans- configurations, with trans- being more than 80% populated. The trans-configuration was established from C5α-P6α correlation and ø and ψ angles of the proline. The five-membered proline ring is in DOWN puckered (C-β-exo/C-γ-endo) conformation. The structure of the peptide reveals that the two cysteine thiols are?5 A° apart and appropriately positioned to covalently bind cis-diamminedichloroplatinum(II), a widely used anti-cancer drug.  相似文献   
619.
620.
Novel Aza-resveratrol analogs were synthesized, structurally characterized and evaluated for cytotoxic activity against MDA-MB-231 and T47D breast cancer cell lines, which exhibited superior inhibitory activity than parent resveratrol compound. The binding mechanism of these compounds with estrogen receptor-α was rationalized by molecular docking studies which indicated additional hydrogen binding interactions and tight binding in the protein cavity. Induction of Beclin-1 protein expression in breast cancer cell lines after treatment with newly synthesized resveratrol analogs indicated inhibition of growth of these cell lines through autophagy. The study highlighted the advantage of introducing the imino-linkage in resveratrol motif in enhancing the anticancer potential of resveratrol suggesting that these analogs can serve as better therapeutic agents against breast cancer and can provide starting point for building more potent analogs in future.  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