全文获取类型
收费全文 | 34480篇 |
免费 | 202篇 |
国内免费 | 321篇 |
专业分类
系统科学 | 269篇 |
丛书文集 | 386篇 |
教育与普及 | 230篇 |
理论与方法论 | 101篇 |
现状及发展 | 14013篇 |
研究方法 | 1257篇 |
综合类 | 18404篇 |
自然研究 | 343篇 |
出版年
2013年 | 354篇 |
2012年 | 570篇 |
2011年 | 872篇 |
2010年 | 342篇 |
2009年 | 346篇 |
2008年 | 704篇 |
2007年 | 722篇 |
2006年 | 704篇 |
2005年 | 696篇 |
2004年 | 686篇 |
2003年 | 731篇 |
2002年 | 795篇 |
2001年 | 1219篇 |
2000年 | 1135篇 |
1999年 | 754篇 |
1994年 | 436篇 |
1992年 | 616篇 |
1991年 | 492篇 |
1990年 | 579篇 |
1989年 | 524篇 |
1988年 | 501篇 |
1987年 | 538篇 |
1986年 | 540篇 |
1985年 | 663篇 |
1984年 | 456篇 |
1983年 | 454篇 |
1982年 | 409篇 |
1981年 | 399篇 |
1980年 | 419篇 |
1979年 | 1006篇 |
1978年 | 792篇 |
1977年 | 727篇 |
1976年 | 614篇 |
1975年 | 686篇 |
1974年 | 847篇 |
1973年 | 748篇 |
1972年 | 725篇 |
1971年 | 906篇 |
1970年 | 1094篇 |
1969年 | 906篇 |
1968年 | 927篇 |
1967年 | 805篇 |
1966年 | 733篇 |
1965年 | 536篇 |
1959年 | 294篇 |
1958年 | 532篇 |
1957年 | 386篇 |
1956年 | 336篇 |
1955年 | 323篇 |
1954年 | 322篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Wai-Hung Ng S F Lee 《厦门大学学报(自然科学版)》2002,(Z1)
With a unique corporate culture based on ancient Ch in ese wisdom being implemented at workplace for more than 10 years, we have been e ncountering various issue of managing conflicts, in particular at organization r estructure period, although we perceive that conflict does not necessarily have dysfunctional effect on our group performance. However, conflicts between and am ong various levels of the organization hierarchy are inevitably creating certain impact on our organization cohesiveness, performa... 相似文献
102.
Acquired immunity and epidemiology of Schistosoma haematobium 总被引:1,自引:0,他引:1
Human immune responses to schistosome infection have been characterized in detail. But there has been controversy over the relative importance of ecological factors (variation in exposure to infection) and immunological factors (acquired immunity) in determining the relationships between levels of infection and age typically found in areas where infection is endemic. Independent effects of exposure and age on the rates of reinfection with Schistosoma haematobium after chemotherapy have been demonstrated in the Gambia and Zimbabwe. This age effect could be the result of acquired immunity to infection. Indeed, allowing for variation in exposure and age, low rates of reinfection in the Gambia are correlated with high amounts of specific IgE antibodies--human IgE can kill S. mansoni schistosomulae in vitro. Further, animals can acquire immunologically mediated resistance to S. mansoni infection, although nonimmunological factors could also be involved. Acquisition of this immunity seems to be related to the cumulative effects of repeated infection and provides only partial protection. These characteristics are consistent with immuno-epidemiological data for both S. mansoni and S. haematobium infections of humans. We have now analysed age-prevalence data for human infection with S. haematobium, and find patterns of variation that are indeed consistent with the epidemiological effects of acquired immunity predicted by mathematical models. 相似文献
103.
常全明 《河北理工学院学报》1994,(1)
论述了冀东金矿集中区绿岩型金矿的矿质来源,并恢复其矿源层的原岩。对构造及中小型岩浆任入体的控矿作用作了论述,并提出了成矿模式。 相似文献
104.
105.
Neurotransmission from mossy fibre terminals onto cerebellar granule cells is almost certainly mediated by L-glutamate. By taking advantage of the small soma size, limited number of processes and short dendrite length of granule cells, we have obtained high-resolution recordings of spontaneous miniature excitatory postsynaptic currents (m.e.p.s.cs) and evoked currents in thin cerebellar slices. Miniature currents have a similar time-course and pharmacology to evoked currents and consist of an exceptionally fast non-NMDA (N-methyl-D-aspartate) component (measured rise-time, 200 microseconds; estimated pre-filtered rise-time less than 100 microseconds; decay time constant, tau = 1.0 ms), followed by 50 pS NMDA channel openings that are directly resolvable. We could find no evidence for the recent proposal that miniature currents in granule cells are mediated solely by NMDA channels with a novel time course. The non-NMDA receptor component of m.e.p.s.cs has a skewed amplitude distribution, which suggests potential complications for quantal analysis. The difference in time course between the m.e.p.s.cs reported here and other synaptic currents in the brain could reflect differences in synaptic function or electrotonic filtering; the relative contribution of these possibilities has yet to be established. 相似文献
106.
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
107.
108.
研究以水泥处理固体有机物时,有机物对水泥水化的影响。以膜流模式说明水份在水泥浆体内传输的现象。水膜存在半干之水泥浆体,其厚度小于100nm,膜流由离分压所驱动,而离分压来自分子间作用力。膜拟结果发现,水泥浆体内局部位置可用以进行水化之水量为Q=-Aslv/6vπ。当有机物添加在水泥浆体内时,会影响Hamaker常数,Aslv因此可能使膜流不稳定或完全抑制膜流,因而使水泥浆体内局部缺水,影响水化进行,造成成品强度降低,影响品质。 相似文献
109.
The highest specific activity of thiamin pyrophosphokinase was found in the cerebellum, and lower activity in cerebral cortex and midbrain. The regional difference in the enzyme activity was similar to that in thiamin content and the influx rate in rat brain, suggesting that the enzyme is involved in the thiamin transport. 相似文献
110.
对径向滑动轴承、推力滑动轴承试验台以及实验台的结构设计、试验范围、功能和工业产品实验进行了介绍。该试验台在滑动轴承的实验研究中得到了很好的应用。 相似文献