全文获取类型
收费全文 | 63362篇 |
免费 | 285篇 |
国内免费 | 554篇 |
专业分类
系统科学 | 1246篇 |
丛书文集 | 522篇 |
教育与普及 | 280篇 |
理论与方法论 | 524篇 |
现状及发展 | 34059篇 |
研究方法 | 1270篇 |
综合类 | 24113篇 |
自然研究 | 2187篇 |
出版年
2013年 | 817篇 |
2012年 | 741篇 |
2011年 | 2855篇 |
2009年 | 618篇 |
2008年 | 942篇 |
2007年 | 1126篇 |
2006年 | 1140篇 |
2005年 | 1370篇 |
2004年 | 2534篇 |
2003年 | 2061篇 |
2002年 | 1768篇 |
2001年 | 1692篇 |
2000年 | 1197篇 |
1999年 | 1161篇 |
1998年 | 643篇 |
1997年 | 778篇 |
1996年 | 537篇 |
1994年 | 697篇 |
1993年 | 694篇 |
1992年 | 1090篇 |
1991年 | 880篇 |
1990年 | 967篇 |
1989年 | 788篇 |
1988年 | 758篇 |
1987年 | 776篇 |
1986年 | 847篇 |
1985年 | 1030篇 |
1984年 | 856篇 |
1983年 | 746篇 |
1982年 | 824篇 |
1981年 | 871篇 |
1980年 | 968篇 |
1979年 | 1609篇 |
1978年 | 1414篇 |
1977年 | 1398篇 |
1976年 | 1199篇 |
1975年 | 1186篇 |
1974年 | 1206篇 |
1973年 | 1356篇 |
1972年 | 1460篇 |
1971年 | 1496篇 |
1970年 | 1753篇 |
1969年 | 1513篇 |
1968年 | 1414篇 |
1967年 | 1319篇 |
1966年 | 1150篇 |
1965年 | 912篇 |
1964年 | 527篇 |
1958年 | 775篇 |
1957年 | 608篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
451.
S. A. Karuppaswamy 《Cellular and molecular life sciences : CMLS》1977,33(6):735-736
Summary The purified chitin from the cuticle of a pentastomid was examined by X-ray method. The X-ray photograph discloses that the chitin in question is of -type. Since the arthropod cuticle contains -chitin, it is suggested that Pentastomida may be considered an independent phylum.Thanks are due to Prof. Dr. G. Sundara Rajulu for guidance and encouragement. 相似文献
452.
For the identification of a peptidyl principle inducing sexual agglutination in the yeast, 2 supposed hexapeptides (1a, b) were synthesized by the conventional method. The 1a (H-Arg-Gly-Pro-Phe-Pro-Ile-OH) revealed complete identity with the natural peptide in TLC, MS and biological property on agglutination. The 1b showed the sexual agglutinability in the same degree as 1a, though distinct differences were observed in the chemical data. Both 1a and 1b had a strong bitter taste. 相似文献
453.
In vivo studies indicated that the primary effects of E. coli endotoxin on hepatic clearance of sulfobromophthalein were at the excretory level. Newborns were more sensitive to the LPS than older animals. 相似文献
454.
455.
456.
Incorporation of 32P into adrenal mitochondrial phospholipids (PL) incrased in ACTH-treated rats, but it decreased in diabetics, inspite of the fact that these animals showed adrenal overacity. Since diabetics did not show increased 11 beta-hydroxylation. as opposed to ACTH-treated rats, it is suggested that the stimulation of this enzyme activity by exogenous ACTH is related to an increased turnover of PL at the mitochondrial membrane. The process is impaired in diabetics and prevents the stimulation of 11 beta-hydroxylation. 相似文献
457.
E. Albert Zeller 《Cellular and molecular life sciences : CMLS》1977,33(2):143-150
Summary Enzymes were the first clearly recognized components of snake venoms. When several more were discovered, attempts were made to correlate venom action with enzymic functions. The last few years have seen most successful efforts in the identification, isolation and structural elucidation of highly toxic polypeptides present in snake venoms, in particular of neurotoxins and membrane-active toxins. Following this development the polypeptides were called the true toxic components and the enzymes lost their previous central position in venom pharmacology. The time, therefore, has come to re-evaluate the role of enzymes in the complex interaction between snake and prey. While highly active polypeptides indeed dominate the action of hydrophiid venoms, they appear to play a lesser role in crotalid venom action as compared with enzyme components. Enzymes are involved in many levels of venom action, e. g. by serving as spreading factors, of by producing very active agents, such as bradykinin and lysolecithins in tissues of preys or predators. Some toxins, e. g. the membrane-active polypeptides appear to participate in the interaction between membrane phospholipids and venom phospholipases. The classical neurotoxin, -bungarotoxin, has been recognized as a powerful phospholipase. Several instances are known which indicate that some enzymes potentiate the toxic action of others; the analysis of a single enzyme may, therefore, not fully reveal its biofunction. For 3 enzymes, ophidianl-amino acid oxidase, ATPpyrophosphatase, and acetylcholinesterase, some of the problems pertaining to venom toxicity are discussed. 相似文献
458.
C. Hegyvary 《Cellular and molecular life sciences : CMLS》1977,33(10):1280-1281
Summary Aldosterone (15 g BID) and methylprednisolone (8 mg QD) administration to female guinea-pigs augmented both the total and the specific activity of NaK-ATPase but not the activity of adenylate cyclase in the cardiac sarcolemma. The rise in NaK-ATPase was due to increase in the number of enzyme molecules; catalytic activity and ouabain-sensitivity of individual molecules did not change.Acknowledgments. This work was supported by grant 1 R01 HL16611 from the National Heart and Lung Institute of the National Institutes of Health, United States Public Health Service. I thank Mr Kooil Kang for his excellent technical assistance. 相似文献
459.
Summary Pronase and -chymotrypsin digested the major glycoprotein in the human and mouse red cell membranes and in SDS gel electrophoresis the glycoprotein disappeared accompanied by the appearance of a new band of lower mol.wt. However in the membranes of sheep, rat and rabbit, no digestion was demonstrated. The effects of pronase on anion permeability were almost identical for human and animal erythrocytes. 相似文献
460.
Summary A convenient one-step procedure, based upon the tyrosinase co-oxidation of dopa and cysteine, is reported for the synthesis of 5-S-cysteinyldopa (I) in 74% yield. Secondary products of the reaction turned out to be 2-S-cysteinyldopa (II, 14%), 2,5-S, S-dicysteinyldopa (IV, 5%), and the hitherto unknown 6-S-cysteinyldopa (III, 1%).The generic term cysteinyldopa is proposed to designate the various cotechol amino-acids arising from addition of cysteine to dopaquinone.This work was supported in part by a grant from Consiglio Nazionale delle Ricerche, Roma. 相似文献