全文获取类型
收费全文 | 15169篇 |
免费 | 28篇 |
国内免费 | 47篇 |
专业分类
系统科学 | 63篇 |
丛书文集 | 181篇 |
教育与普及 | 32篇 |
理论与方法论 | 74篇 |
现状及发展 | 6183篇 |
研究方法 | 792篇 |
综合类 | 7630篇 |
自然研究 | 289篇 |
出版年
2013年 | 105篇 |
2012年 | 266篇 |
2011年 | 549篇 |
2010年 | 105篇 |
2008年 | 325篇 |
2007年 | 304篇 |
2006年 | 323篇 |
2005年 | 330篇 |
2004年 | 319篇 |
2003年 | 281篇 |
2002年 | 262篇 |
2001年 | 459篇 |
2000年 | 442篇 |
1999年 | 312篇 |
1992年 | 268篇 |
1991年 | 197篇 |
1990年 | 224篇 |
1989年 | 219篇 |
1988年 | 223篇 |
1987年 | 220篇 |
1986年 | 206篇 |
1985年 | 293篇 |
1984年 | 230篇 |
1983年 | 158篇 |
1982年 | 167篇 |
1981年 | 152篇 |
1980年 | 181篇 |
1979年 | 418篇 |
1978年 | 309篇 |
1977年 | 307篇 |
1976年 | 290篇 |
1975年 | 323篇 |
1974年 | 385篇 |
1973年 | 364篇 |
1972年 | 379篇 |
1971年 | 434篇 |
1970年 | 550篇 |
1969年 | 463篇 |
1968年 | 469篇 |
1967年 | 433篇 |
1966年 | 384篇 |
1965年 | 285篇 |
1964年 | 87篇 |
1959年 | 170篇 |
1958年 | 297篇 |
1957年 | 199篇 |
1956年 | 185篇 |
1955年 | 150篇 |
1954年 | 185篇 |
1948年 | 138篇 |
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
41.
J A Martignetti A A Aqeel W A Sewairi C E Boumah M Kambouris S A Mayouf K V Sheth W A Eid O Dowling J Harris M J Glucksman S Bahabri B F Meyer R J Desnick 《Nature genetics》2001,28(3):261-265
The inherited osteolyses or 'vanishing bone' syndromes are a group of rare disorders of unknown etiology characterized by destruction and resorption of affected bones. The multicentric osteolyses are notable for interphalangeal joint erosions that mimic severe juvenile rheumatoid arthritis (OMIMs 166300, 259600, 259610 and 277950). We recently described an autosomal recessive form of multicentric osteolysis with carpal and tarsal resorption, crippling arthritic changes, marked osteoporosis, palmar and plantar subcutaneous nodules and distinctive facies in a number of consanguineous Saudi Arabian families. We localized the disease gene to 16q12-21 by using members of these families for a genome-wide search for homozygous-by-descent microsatellite markers. Haplotype analysis narrowed the critical region to a 1.2-cM region that spans the gene encoding MMP-2 (gelatinase A, collagenase type IV; (ref. 3). We detected no MMP2 enzymatic activity in the serum or fibroblasts of affected family members. We identified two family-specific homoallelic MMP2 mutations: R101H and Y244X. The nonsense mutation effects a deletion of the substrate-binding and catalytic sites and the fibronectin type II-like and hemopexin/TIMP2 binding domains. Based on molecular modeling, the missense mutation disrupts hydrogen bond formation within the highly conserved prodomain adjacent to the catalytic zinc ion. 相似文献
42.
R.E. Kastner 《Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics》2005,36(4):649-658
A modified version of Young's experiment by Shahriar Afshar demonstrates that, prior to what appears to be a “which-way” measurement, an interference pattern exists. Afshar has claimed that this result constitutes a violation of the Principle of Complementarity. This paper discusses the implications of this experiment and considers how Cramer's Transactional Interpretation easily accommodates the result. It is also shown that the Afshar experiment is analogous in key respects to a spin one-half particle prepared as “spin up along x”, subjected to a nondestructive confirmation of that preparation, and post-selected in a specific state of spin along z. The terminology “which-way” or “which-slit” is critiqued; it is argued that this usage by both Afshar and his critics is misleading and has contributed to confusion surrounding the interpretation of the experiment. Nevertheless, it is concluded that Bohr would have had no more problem accounting for the Afshar result than he would in accounting for the aforementioned pre- and post-selection spin experiment, in which the particle's preparation state is confirmed by a nondestructive measurement prior to post-selection. In addition, some new inferences about the interpretation of delayed choice experiments are drawn from the analysis. 相似文献
43.
H. -P. Lipp H. Schwegler W. E. Crusio D. P. Wolfer M. -C. Leisinger-Trigona B. Heimrich P. Driscoll 《Cellular and molecular life sciences : CMLS》1989,45(9):845-859
Summary Genetically-defined rodent strains permit the identification of hippocampal traits which are of functional relevance for the performance of two-way avoidance behavior. This is exemplified here by analyzing the relationship between infrapyramidal mossy fibers (a tiny projection terminating upon the basal dendrites of hippocampal pyramidal neurons) and two-way avoidance learning in about 800 animals. The necessary steps include 1) identification of structural traits sensitive to selective breeding for extremes in two-way avoidance, 2) testing the robustness of the associations found by studying individual and genetical correlations between hippocampal traits and behavior, 3) establishing causal relationships by Mendelian crossing of strains with extreme structural traits and studying the behavioral consequences of such structural randomization, 4) confirming causal relationships by manipulating the structural variable in inbred (isogenic) strains, thereby eliminating the possibility of genetic linkage, and 5) ruling out the possibility of spurious associations by studying the correlations between the hippocampal trait and other behaviors known to depend on hippocampal functioning.In comparison with the classical lesion approach for identifying relationships between brain and behavior, the present procedure appears to be superior in two aspects: it is non-invasive, and it focuses automatically on those brain traits which are used by natural selection to shape behaviorally-defined animal populations, i.e., it reveals the natural regulators of behavior. 相似文献
44.
J. P. J. Billen B. D. Jackson E. D. Morgan 《Cellular and molecular life sciences : CMLS》1988,44(9):794-797
Summary The principal constituent of the pygidial gland ofNothomyrmecia macrops is 3,7-dimethyloct-6-en-2-one, a substance not previously identified in insects. Also identified were 2,6-dimethylhept-5-enal, 2-nonanone, indole, -dodecalactone, and the hydrocarbons pentadecane, heptadecane, heptadecene and heptadecadiene, all in low nanogram quantities. 相似文献
45.
B. Lindblad W. E. Burkel T. W. Wakefield L. M. Graham J. C. Stanley 《Cellular and molecular life sciences : CMLS》1988,44(3):223-224
Summary The most important effect of dihydroergotamine is venoconstriction, but certain metabolic effects and changes in vessel prostanoid activity have also been suggested. In this study endothelial cell production of 6-keto PGF1 and TxB2 was quantitated in vitro. No evidence of altered prostanoid production was noted after incubation with dihydroergotamine (exposure ranging from 5×10–3 to 5×10–7 g/l). Similarly, no effect of dihydroergotamine on the growth rates of endothelial cells or smooth muscle cells in vitro was documented. 相似文献
46.
E. Habermann 《Cellular and molecular life sciences : CMLS》1988,44(3):224-226
Summary Rat brain homogenate was preloaded with [3H]noradrenaline or [3H]GABA and stimulated with high K+. Tetanus toxin and botulinum A neurotoxin partially prevent the evoked [3H]noradrenaline release in the same range of toxin concentrations starting below 10–10M. In contrast, release of -amino butyric acid (GABA) is much more sensitive to tetanus than to botulinum A toxin. 相似文献
47.
E. Flückiger U. Briner B. Clark A. Closse A. Enz P. Gull A. Hofmann R. Markstein L. Tolcsvai H. R. Wagner 《Cellular and molecular life sciences : CMLS》1988,44(5):431-436
Summary The profile of action in animals of CQP 201-403, a novel 8-amino-ergoline, is in most aspects that of a very potent dopaminomimetic, both as a prolactin secretion inhibitor, and at the levels of the CNS and the cardiovascular system. Qualitatively CQP 201-403 differs slightly from bromocriptine and apomorphine in its effects on the CNS (no influence on serotonin metabolism in the rat cortex; induction of masculine mounting behavior in rats) and the cardiovascular system of the dog (reflex tachycardia in response to a blood-pressure fall). In man the new compound proved to be highly active in lowering prolactin serum levels and to be more potent than bromocriptine (Parlodel®).In memory of Dr Annemarie Closse, who died 14 June 1987. 相似文献
48.
Definition of a consensus binding site for p53. 总被引:35,自引:0,他引:35
Recent experiments have suggested that p53 action may be mediated through its interaction with DNA. We have now identified 18 human genomic clones that bind to p53 in vitro. Precise mapping of the binding sequences within these clones revealed a consensus binding site with a striking internal symmetry, consisting of two copies of the 10 base pair motif 5'-PuPuPuC(A/T)(T/A)GPyPyPy-3' separated by 0-13 base pairs. One copy of the motif was insufficient for binding, and subtle alterations of the motif, even when present in multiple copies, resulted in loss of affinity for p53. Mutants of p53, representing each of the four "hot spots" frequently altered in human cancers, failed to bind to the consensus dimer. These results define the DNA sequence elements with which p53 interacts in vitro and which may be important for p53 action in vivo. 相似文献
49.
A E Davis K Aulak R B Parad H P Stecklein E Eldering C E Hack J Kramer R C Strunk J Bissler F S Rosen 《Nature genetics》1992,1(5):354-358
Heterozygosity for a mutant dysfunctional C1 inhibitor protein, a member of the serine proteinase inhibitor (serpin) superfamily, results in type II hereditary angioneurotic oedema. We identified a "hinge" region mutation in C1 inhibitor with a Val to Glu replacement at P14 Val-432. Recombinant C1 inhibitors P10 Ala-->Thr and P14Val-->Glu did not form stable complexes with fluid phase C1s or kallikrein. The P14 Val-->Glu mutant, however, was cleaved to a 96K form by C1s, while the P10 Ala-->Thr mutant was not. The recombinant P10 mutant also did not complex with C1s, kallikrein or beta-factor Xlla-Sepharose. The two mutations, therefore, result in dysfunction by different mechanisms: in one (P14 Val-->Glu), the inhibitor is converted to a substrate, while in the other (P10 Ala-->Thr), interaction with target protease is blocked. 相似文献
50.
Summary By comparing steroid sulphatase levels per se, and also ratios to -galactosidase, in 6 sets of mice — normal females, entire and castrated males both with and without exogenous testosterone administration — we obtained support for the contention that induction of this enzyme is in part controlled by male hormones. 相似文献