全文获取类型
收费全文 | 20813篇 |
免费 | 51篇 |
国内免费 | 56篇 |
专业分类
系统科学 | 80篇 |
丛书文集 | 280篇 |
教育与普及 | 33篇 |
理论与方法论 | 73篇 |
现状及发展 | 9854篇 |
研究方法 | 869篇 |
综合类 | 9542篇 |
自然研究 | 189篇 |
出版年
2013年 | 124篇 |
2012年 | 267篇 |
2011年 | 455篇 |
2008年 | 285篇 |
2007年 | 322篇 |
2006年 | 352篇 |
2005年 | 347篇 |
2004年 | 456篇 |
2003年 | 321篇 |
2002年 | 333篇 |
2001年 | 607篇 |
2000年 | 537篇 |
1999年 | 395篇 |
1994年 | 93篇 |
1992年 | 365篇 |
1991年 | 274篇 |
1990年 | 295篇 |
1989年 | 284篇 |
1988年 | 264篇 |
1987年 | 293篇 |
1986年 | 323篇 |
1985年 | 408篇 |
1984年 | 303篇 |
1983年 | 288篇 |
1982年 | 255篇 |
1981年 | 260篇 |
1980年 | 281篇 |
1979年 | 700篇 |
1978年 | 595篇 |
1977年 | 532篇 |
1976年 | 438篇 |
1975年 | 509篇 |
1974年 | 677篇 |
1973年 | 551篇 |
1972年 | 566篇 |
1971年 | 674篇 |
1970年 | 862篇 |
1969年 | 667篇 |
1968年 | 673篇 |
1967年 | 645篇 |
1966年 | 547篇 |
1965年 | 458篇 |
1964年 | 153篇 |
1959年 | 224篇 |
1958年 | 385篇 |
1957年 | 290篇 |
1956年 | 224篇 |
1955年 | 222篇 |
1954年 | 232篇 |
1948年 | 153篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
31.
Abnormal pattern detected in fragile-X patients by pulsed-field gel electrophoresis. 总被引:26,自引:0,他引:26
The fragile-X syndrome is the most frequent inherited form of mental retardation, with an incidence of 1 in 1,500 males. It is characterized by the presence of a fragile site at Xq27.3 induced in vitro by folate deprivation or by inhibitors of deoxynucleotide synthesis. Its mode of inheritance is unusual for an X-linked trait, with incomplete penetrance in both males and females. Some phenotypically normal males transmit the mutation to all their daughters who rarely express any symptoms, but penetrance is high in sons and daughters of these carrier women. Genetic and physical mapping of the Xq27-q28 region has confirmed that the disease locus is located at or very near the fragile site. Hypotheses proposed to account for the abnormalities in the inheritance of the disease include sequence rearrangements by meiotic recombination or a mutation that affects reactivation of an inactive X chromosome during differentiation of female germ cells. To detect such rearrangements, or methylation changes that may reflect a locally inactive X chromosome, we used pulsed-field gel analysis of DNA from fragile-X patients with probes close to the fragile-X locus. The probe Do33 (DXS465) detected abnormal patterns in fragile-X patients, but not in normal controls or in non-expressing male transmitters. 相似文献
32.
Summary Immunohistochemistry revealed an Ig-A-like substance on the luminal surface of the pineal follicles and in the parafollicular layer. This substance was observed around 1 week of age and disappeared by 8 weeks at the time when the transformation of the follicular pattern leads to an adult-type pineal tissue. 相似文献
33.
Chromosomal effects of adeno-associated virus vector integration. 总被引:17,自引:0,他引:17
Adeno-associated virus (AAV) vectors are currently being used in several clinical gene-therapy trials (see the NIH OBA Human Gene Transfer Clinical Trials Database); however, little is known about the chromosomal effects of vector integration. Here we report that integrated vector proviruses are associated with chromosomal deletions and other rearrangements and are frequently located on chromosome 19 (although not at the wildtype AAV integration site). 相似文献
34.
We discuss a generalization of the standard notion of probability space and show that the emerging framework, to be called operational probability theory, can be considered as underlying quantal theories. The proposed framework makes special reference to the convex structure of states and to a family of observables which is wider than the familiar set of random variables: it appears as an alternative to the known algebraic approach to quantum probability. 相似文献
35.
就近几年图书馆界关于新世纪馆员意识转换及社会角色转换等方面的研究进行了综述,指出新时期的馆员要实现自我社会角色的转换,首先是要明确转换的必要性,然后采取有效的策略逐步地、系统地推进转换,才能取得较好的效果。 相似文献
36.
37.
Coalignment of vimentin intermediate filaments with microtubules depends on kinesin. 总被引:19,自引:0,他引:19
Intermediate filaments in most types of cultured cells coalign with microtubules. Depolymerization of microtubules results in collapse of vimentin and desmin intermediate filaments to the nucleus where they form a perinuclear cap. Collapse can also be induced by microinjection of antibodies against intermediate filament or microtubule proteins. Thus, two filament systems interact with each other. But the molecules mediating this interaction are unknown. One of the candidates for this role is a microtubule motor kinesin. Recent data showed that kinesin is involved in the plus end-directed movement of the membranous organelles along microtubules such as radial extension of lysosomes in macrophages and centrifugal movement of pigment in melanophores. Here we report that injection of the anti-kinesin antibody into human fibroblasts results in the redistribution of intermediate filaments to a tight perinuclear aggregate but had no effect on the distribution of microtubules. Thus, kinesin is involved not only in organelle movement but also in interaction of the two major cytoskeletal systems, intermediate filaments and microtubules. 相似文献
38.
C. Ambrogi Lorenzini C. Bucherelli A. Giachetti G. Tassoni 《Cellular and molecular life sciences : CMLS》1991,47(10):1019-1026
Several aspects of spontaneous and conditioned behavior (food and water intake, locomotion and emotionality, passive and active avoidance acquisition and retention) of standard (albino and pigmented) rats, and rats heterozygous (HEDI) and homozygous (HODI) for diabetes insipidus, are reviewed. As would be expected, HODI rats have been repeatedly found to consume far more fluid than either HEDI or control rats. Pigmented rats appear to be more active than albinos. HODI rats exhibit less marked emotional responses than do control rats, among which the pigmented ones exhibit the highest emotionality. Light aversion is more evident in albino than in pigmented rats. No differences are found among HEDI, HODI and normal Long Evans rats. It is quite difficult to provide a clear-cut statement concerning inter-strain differences in passive avoidance behavior, possibly because of the variety of techniques employed. In any case, HODI rats do not perform worse than normal controls do. In one-way active avoidance paradigms, pigmented rats perform better than albinos, and the performance of HODI rats does not differ from that of controls. In two-way avoidance paradigms, albinos appear to outperform pigmented rats. Once again, there are no obvious differences between HODI and control animals.In addition to indicating that HODI rats may actually be less emotional than the other groups of rats reviewed here, the studies described once again fail to confirm the previously alleged functions of vasopressin in memory consolidation. 相似文献
39.
We investigated the sound communication associated with mating inNezara viridula (L.) to clarify conflicting reports on the medium through which acoustic signals are borne. Recordings made from virgin pairs ofN. viridula during precopulatory and compulatory behaviour have revealed that signals transmitted as vibrations through the substrate are a more likely means of communication than signals transmitted by a radiation of sound pressure waves through the air (at least in Australian populations). We present evidence (additional to that already in the literature) that air-borne acoustics are an unlikely mechanism of sexual communication in this species. Specifically, the recorded pulse train patterns showed no consistency or repeatability in relation to different stages of mating behaviour. In contrast, frequency spectrograms of substrate-borne signals reveal repeatable patterns that do correspond with the stage of mating behaviour. 相似文献
40.