全文获取类型
收费全文 | 71730篇 |
免费 | 1943篇 |
国内免费 | 2880篇 |
专业分类
系统科学 | 2212篇 |
丛书文集 | 2224篇 |
教育与普及 | 1943篇 |
理论与方法论 | 279篇 |
现状及发展 | 4588篇 |
研究方法 | 663篇 |
综合类 | 64366篇 |
自然研究 | 278篇 |
出版年
2023年 | 644篇 |
2022年 | 980篇 |
2021年 | 1029篇 |
2020年 | 764篇 |
2019年 | 319篇 |
2018年 | 598篇 |
2017年 | 670篇 |
2016年 | 774篇 |
2015年 | 1518篇 |
2014年 | 2155篇 |
2013年 | 2108篇 |
2012年 | 2536篇 |
2011年 | 3245篇 |
2010年 | 2782篇 |
2009年 | 3061篇 |
2008年 | 3581篇 |
2007年 | 3456篇 |
2006年 | 2895篇 |
2005年 | 2930篇 |
2004年 | 2183篇 |
2003年 | 2129篇 |
2002年 | 2191篇 |
2001年 | 2376篇 |
2000年 | 2213篇 |
1999年 | 3108篇 |
1998年 | 2416篇 |
1997年 | 2443篇 |
1996年 | 2328篇 |
1995年 | 1916篇 |
1994年 | 1799篇 |
1993年 | 1478篇 |
1992年 | 1454篇 |
1991年 | 1348篇 |
1990年 | 1127篇 |
1989年 | 1094篇 |
1988年 | 904篇 |
1987年 | 625篇 |
1986年 | 427篇 |
1985年 | 332篇 |
1979年 | 334篇 |
1978年 | 259篇 |
1977年 | 244篇 |
1974年 | 309篇 |
1973年 | 279篇 |
1971年 | 340篇 |
1970年 | 475篇 |
1969年 | 329篇 |
1968年 | 316篇 |
1967年 | 320篇 |
1966年 | 349篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
81.
廊坊市“文化信息资源共享工程”建设分析与研究 总被引:1,自引:1,他引:0
在介绍廊坊市“文化信息资源共享工程”建设现状基础上,阐述了资源共享的意义,分析了资源共享存在的问题,研究了相应的解决方法。 相似文献
82.
83.
84.
W. Jadassohn E. Cherbuliez P. Boymond H. Isler 《Cellular and molecular life sciences : CMLS》1948,4(6):225-226
Summary The authors show the antibiotic activity of water-insoluble salts of hydrosoluble antibiotics in the case of penicillin G (salts of iron, copper, silver, gold, and uranium) and streptomycin (oleate). 相似文献
85.
目的建立高效液相色谱法(HPLC)测定复方盐酸普莫卡因乳膏含量的方法。方法选用CLC-ODS C18色谱柱(150 mm×4.6 mm,5μm),流动相为乙腈-磷酸盐缓冲液(55∶45,体积比)调节pH值为7.5,流速为1.0 mL/min,柱温为40℃,检测波长为224 nm。结果盐酸普莫卡因在0.212 0~0.903 5 mg/mL范围内浓度与峰面积呈良好线性关系(r=0.999 9),平均回收率为99.63%,RSD为0.53%。结论该法简便、快速、可靠,可用于复方盐酸普莫卡因乳膏的质量控制。 相似文献
86.
通过明确学习目标,激发学习意愿;对钳工实训目标分解,做到心中有数.培养打牢基本技能基础,注重综合操作训练.为适应市场需求,重视素质培养. 相似文献
87.
Houlden H Johnson J Gardner-Thorpe C Lashley T Hernandez D Worth P Singleton AB Hilton DA Holton J Revesz T Davis MB Giunti P Giunti P Wood NW 《Nature genetics》2007,39(12):1434-1436
The microtubule-associated protein tau (encoded by MAPT) and several tau kinases have been implicated in neurodegeneration, but only MAPT has a proven role in disease. We identified mutations in the gene encoding tau tubulin kinase 2 (TTBK2) as the cause of spinocerebellar ataxia type 11. Affected brain tissue showed substantial cerebellar degeneration and tau deposition. These data suggest that TTBK2 is important in the tau cascade and in spinocerebellar degeneration. 相似文献
88.
89.
Tissue-specific and reversible RNA interference in transgenic mice 总被引:11,自引:0,他引:11
Dickins RA McJunkin K Hernando E Premsrirut PK Krizhanovsky V Burgess DJ Kim SY Cordon-Cardo C Zender L Hannon GJ Lowe SW 《Nature genetics》2007,39(7):914-921
Genetically engineered mice provide powerful tools for understanding mammalian gene function. These models traditionally rely on gene overexpression from transgenes or targeted, irreversible gene mutation. By adapting the tetracycline (tet)-responsive system previously used for gene overexpression, we have developed a simple transgenic system to reversibly control endogenous gene expression using RNA interference (RNAi) in mice. Transgenic mice harboring a tet-responsive RNA polymerase II promoter driving a microRNA-based short hairpin RNA targeting the tumor suppressor Trp53 reversibly express short hairpin RNA when crossed with existing mouse strains expressing general or tissue-specific 'tet-on' or 'tet-off' transactivators. Reversible Trp53 knockdown can be achieved in several tissues, and restoring Trp53 expression in lymphomas whose development is promoted by Trp53 knockdown leads to tumor regression. By leaving the target gene unaltered, this approach permits tissue-specific, reversible regulation of endogenous gene expression in vivo, with potential broad application in basic biology and drug target validation. 相似文献
90.
Komen JC Distelmaier F Koopman WJ Wanders RJ Smeitink J Willems PH 《Cellular and molecular life sciences : CMLS》2007,64(24):3271-3281
Refsum disease is a rare, inherited neurodegenerative disorder characterized by accumulation of the dietary branched-chain
fatty acid phytanic acid in plasma and tissues caused by a defect in the alphaoxidation pathway. The accumulation of phytanic
acid is believed to be the main pathophysiological cause of the disease. However, the exact mechanism(s) by which phytanic
acid exerts its toxicity have not been resolved. In this study, the effect of phytanic acid on mitochondrial respiration was
investigated. The results show that in digitonin-permeabilized fibroblasts, phytanic acid decreases ATP synthesis, whereas
substrate oxidation per se is not affected. Importantly, studies in intact fibroblasts revealed that phytanic acid decreases both the mitochondrial
membrane potential and NAD(P)H autofluorescence. Taken together, the results described here show that unesterified phytanic
acid exerts its toxic effect mainly through its protonophoric action, at least in human skin fibroblasts.
Received 4 August 2007; received after revision 26 September 2007; accepted 10 October 2007
J. C. Komen, F. Distelmaier: These authors contributed equally to this work. 相似文献