全文获取类型
收费全文 | 17687篇 |
免费 | 59篇 |
国内免费 | 87篇 |
专业分类
系统科学 | 74篇 |
丛书文集 | 121篇 |
教育与普及 | 45篇 |
理论与方法论 | 41篇 |
现状及发展 | 7452篇 |
研究方法 | 862篇 |
综合类 | 9039篇 |
自然研究 | 199篇 |
出版年
2013年 | 145篇 |
2012年 | 276篇 |
2011年 | 450篇 |
2009年 | 115篇 |
2008年 | 345篇 |
2007年 | 391篇 |
2006年 | 392篇 |
2005年 | 383篇 |
2004年 | 337篇 |
2003年 | 356篇 |
2002年 | 311篇 |
2001年 | 688篇 |
2000年 | 673篇 |
1999年 | 412篇 |
1994年 | 312篇 |
1992年 | 385篇 |
1991年 | 273篇 |
1990年 | 332篇 |
1989年 | 291篇 |
1988年 | 254篇 |
1987年 | 313篇 |
1986年 | 313篇 |
1985年 | 386篇 |
1984年 | 279篇 |
1983年 | 264篇 |
1982年 | 246篇 |
1981年 | 226篇 |
1980年 | 217篇 |
1979年 | 597篇 |
1978年 | 434篇 |
1977年 | 402篇 |
1976年 | 350篇 |
1975年 | 357篇 |
1974年 | 433篇 |
1973年 | 393篇 |
1972年 | 352篇 |
1971年 | 415篇 |
1970年 | 569篇 |
1969年 | 433篇 |
1968年 | 446篇 |
1967年 | 412篇 |
1966年 | 383篇 |
1965年 | 287篇 |
1959年 | 145篇 |
1958年 | 242篇 |
1957年 | 155篇 |
1956年 | 154篇 |
1955年 | 138篇 |
1954年 | 140篇 |
1948年 | 124篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
281.
The synthesis and initial applications are reported for 1-[p-(palmitamido)-phenyl]ethylenedinitrilotetraacetic acid. The results demonstrate the versatility of this spectroscopic probe molecule, which allows choice of a particular technique for a particular system as well as use of multiple spectroscopic techniques for complementary information about hydrophobic regions in biological systems. 相似文献
282.
The enzymic activity of Mg2+- or Ca2+-stimulated ATPase from Escherichia coli was inhibited by one of the troponin components, TN-I, and by mitochondrial ATPase inhibitor (F1-inhibitor). The inhibitory ability of component TN-I against Mg2+-stimulated AtPase activity was lost after digestion of component TN-I with trypsin. The Mg2+-stimulated ATPase activity inhibited by component TN-I was completely restored by the addition of another troponin component TN-C. 相似文献
283.
Two insect development inhibitors against Drosophila melanogaster have been isolated from the leaves of X. canadense and identified as xanthumin and 8-epi-xanthatin. 相似文献
284.
M L Kashyap S G de Mendoza M Campbell C Y Chen R F Lutmer C J Glueck 《Experientia》1978,34(8):1044-1045
Marked urinary loss of lipoprotein lipase activator in experimental rat nephrotic syndrome may be partly responsible for its deficiency in plasma very low density lipoproteins. 相似文献
285.
A simple method is described to collect cervical smears and to have a clear view of cervix for small breed of monkeys. This method was found useful to collect adequate cytology smears with good preservation of cellular morphology. 相似文献
286.
A new procedure utilizing dried blood spots was developed for detecting glutathione peroxidase deficiency. Samples from a known patient with a partial defect and from rats with an induced deficiency were distinguished from respective control groups by their longer defluorescence endpoints. Samples from 100 patients with anemia and 2 phenyl-ketonuric infants on low-protein diets contained glutathione peroxidase activity similar to that in 82 controls, when screened for the enzyme defect by the new procedure. 相似文献
287.
Methallibure treatment of mature Cyprinus carpio causes a marked reduction in the steroidogenesis, as indicated by the fall in 3beta-HSD activity in the gonads. Significance of these results is discussed. 相似文献
288.
The activity of dopamine-beta-hydroxylase was measured in the serum before and immediately after electroconvulsive treatments. No significant difference was observed, suggesting that the seizures did not cause an increase in the peripheral sympathetic tone. 相似文献
289.
Our results indicate that pig lymphocytes in culture complete their 1st division at 24 h. At 36 h there are 9% of cells in 2nd division. 3rd mitosis appears at 48 h; and at 72 h there are cells engaged in the 4th division. 相似文献
290.
Distribution of calcitonin cells in the thyroid glands of normal adult rhesus monkey Macaca mulatta.
The calcitonin cells of adult rhesus monkey Macaca mulatta are located in the central region of thyroid along the median axis. The anterior and posterior poles, the isthmus and peripheral regions of thyroid are completely devoid of C cells. The parathyroid also lacks C cells. 相似文献