全文获取类型
收费全文 | 42846篇 |
免费 | 449篇 |
国内免费 | 669篇 |
专业分类
系统科学 | 571篇 |
丛书文集 | 910篇 |
教育与普及 | 315篇 |
理论与方法论 | 170篇 |
现状及发展 | 14837篇 |
研究方法 | 1389篇 |
综合类 | 25364篇 |
自然研究 | 408篇 |
出版年
2014年 | 414篇 |
2013年 | 560篇 |
2012年 | 805篇 |
2011年 | 1241篇 |
2010年 | 538篇 |
2009年 | 660篇 |
2008年 | 1079篇 |
2007年 | 1209篇 |
2006年 | 1015篇 |
2005年 | 1023篇 |
2004年 | 952篇 |
2003年 | 843篇 |
2002年 | 857篇 |
2001年 | 1393篇 |
2000年 | 1354篇 |
1999年 | 1344篇 |
1998年 | 655篇 |
1997年 | 712篇 |
1996年 | 641篇 |
1995年 | 553篇 |
1994年 | 536篇 |
1993年 | 458篇 |
1992年 | 986篇 |
1991年 | 788篇 |
1990年 | 805篇 |
1989年 | 761篇 |
1988年 | 712篇 |
1987年 | 715篇 |
1986年 | 590篇 |
1985年 | 687篇 |
1984年 | 530篇 |
1983年 | 407篇 |
1981年 | 399篇 |
1980年 | 502篇 |
1979年 | 989篇 |
1978年 | 845篇 |
1977年 | 810篇 |
1976年 | 663篇 |
1975年 | 681篇 |
1974年 | 912篇 |
1973年 | 827篇 |
1972年 | 835篇 |
1971年 | 920篇 |
1970年 | 1145篇 |
1969年 | 881篇 |
1968年 | 879篇 |
1967年 | 858篇 |
1966年 | 746篇 |
1965年 | 520篇 |
1958年 | 474篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
51.
Kang J.Y. Xu F.C. 《中国科学基金(英文版)》2004,(2):57-58,64
1 Introduction
Nanoscale science and technology have attracted greatattention since the novel properties become dominant for well-known materials as their sizes reduced to some critical dimension. These properties frequently originate in lattice distortions, structure transformations etc[1]. The variations of size and structure ofnanocrystals lead to the change of their electronic structures. Very recently, nanoscale materials with different electronic structures were utilized in fabricating nanoscale junctions[2].
…… 相似文献
52.
分光光度法测定脯氨酸的含量 总被引:1,自引:0,他引:1
文章用分光光度法研究了脯氨酸与四氯对苯醌的荷移反应 .实验指出 ,在硼砂缓冲溶液中 ,脯氨酸与四氯对苯醌于 30℃的水浴中恒温 1 2 0 min,可形成 1∶ 1的稳定络合物 ,其λmax=35 8nm,表观摩尔吸光系数 ε=1 .5 0× 1 0 5L·mol- 1 ·cm- 1 ,在 60 ng·m L- 1 ~ 40 0 ng·m L- 1 的范围内符合比耳定律 ,用本方法测定药物制剂的含量与文献方法一致 ,回收率在 99.65 %~ 1 0 0 .7%范围内 ,相对标准偏差在 1 .4%以内 . 相似文献
53.
朱惠菊 《首都师范大学学报(自然科学版)》2004,(Z2)
主要就多年来自己在红外光谱分析仪管理和使用中的一些体会进行总结 .科学管理、积极推广 ,提高仪器的使用率 ;精心设计实验内容 ,培养学生解谱能力 ;不断学习新技术、新方法 ,努力提高自身水平 ,充分发挥科学仪器在教学、科研及科技开发工作中的作用 . 相似文献
54.
在综合考虑磁悬浮长大干线特点基础上,参考高速铁路车站的类型特点,根据磁悬浮线路特点和在长大干线上磁悬浮列车的运行特点,从磁悬浮车站的分类、站型设计和站场相关参数的计算等方面探讨了磁悬浮长大干线车站的设计. 相似文献
55.
56.
It is well known that transmitter secretion requires specialized secretory organelles, the synaptic vesicles, for the packaging, storage and exocytotic release of the transmitter. Here we report that when acetylcholine (ACh) is loaded into an isolated Xenopus myocyte, there is spontaneous quantal release of ACh from the myocyte which results in activation of its own surface ACh channels and the appearance of membrane currents resembling miniature endplate currents. This myocyte secretion probably reflects Ca(2+)-regulated exocytosis of ACh-filled cytoplasmic compartments. Furthermore, step depolarization of the myocyte membrane triggers evoked ACh release from the myocyte with a weak excitation-secretion coupling. These findings suggest that quantal transmitter secretion does not require secretory pathways unique to neurons and that the essence of presynaptic differentiation may reside in the provision of transmitter supply and modification of the preexisting secretion pathway. 相似文献
57.
提出了利用上位机参与实时控制,综合分析在线参数、离线参数和间接参数,辅助发酵过程工艺研究和优化控制,并给出了上位机软件包的部分源程序及框图。该软件包对发酵工艺人员进一步了解菌种的遗传特性、细胞代谢调节和反应器工程特性方面有较大帮助。 相似文献
58.
By using optical microstructure(OM), X-ray diffractometer analyses and mechanical properties testing, the abnormal damage of pipe coil in remaining heat boiler has been investigated. The damage is the result of the melting of tube base metal at high temperature caused by the ignition inside the tube. 相似文献
59.
Human cytomegalovirus UL97 open reading frame encodes a protein that phosphorylates the antiviral nucleoside analogue ganciclovir. 总被引:32,自引:0,他引:32
Human cytomegalovirus (HCMV, a betaherpes virus) is the cause of serious disease in immunologically compromised individuals, including those with acquired immunodeficiency syndrome. One of the compounds used in the chemotherapy of HCMV infections is the nucleoside analogue 9-(1,3-dihydroxy-2-propoxymethyl)-guanine (ganciclovir). The mechanism of action of this drug is dependent on the formation of the nucleoside triphosphate, which is a strong inhibitor of the viral DNA polymerase. Thymidine kinase, which is encoded by many of the herpesviruses, catalyses the initial phosphorylation of ganciclovir. But there is no evidence for the coding of this enzyme by HCMV, and DNA sequence analysis of the HCMV genome has shown that there is no open reading frame characteristic of a herpesvirus thymidine kinase. Here we present biochemical and immunological evidence that the HCMV UL97 open reading frame codes for a protein capable of phosphorylating ganciclovir. This protein seems to be responsible for the selectivity of ganciclovir and will be useful tool in the understanding and refinement of the antiviral activity of new selective anti-HCMV compounds. 相似文献
60.
A. F. McDonagh Y. -M. Pu D. A. Lightner 《Cellular and molecular life sciences : CMLS》1992,48(3):246-248
The characteristic circular dichroism of bilirubin bound to human serum albumin undergoes a remarkable sign inversion on addition of halothane, chloroform and other volatile anesthetics. This sign inversion, which is completely reversed by removal of the anesthetic, reflects a pronounced conformational change of the bound ligand; probably a complete inversion of chirality. The observation suggests that association of volatile anesthetics with proteins can markedly alter the internal topography of receptor sites and potentially influence the stereoselectivity of ligand binding. 相似文献