全文获取类型
收费全文 | 30685篇 |
免费 | 69篇 |
国内免费 | 107篇 |
专业分类
系统科学 | 117篇 |
丛书文集 | 419篇 |
教育与普及 | 86篇 |
理论与方法论 | 115篇 |
现状及发展 | 14539篇 |
研究方法 | 1103篇 |
综合类 | 14169篇 |
自然研究 | 313篇 |
出版年
2013年 | 148篇 |
2012年 | 335篇 |
2011年 | 631篇 |
2008年 | 428篇 |
2007年 | 468篇 |
2006年 | 483篇 |
2005年 | 491篇 |
2004年 | 607篇 |
2003年 | 493篇 |
2002年 | 479篇 |
2001年 | 802篇 |
2000年 | 819篇 |
1999年 | 551篇 |
1994年 | 366篇 |
1992年 | 493篇 |
1991年 | 401篇 |
1990年 | 459篇 |
1989年 | 427篇 |
1988年 | 415篇 |
1987年 | 463篇 |
1986年 | 512篇 |
1985年 | 627篇 |
1984年 | 420篇 |
1983年 | 434篇 |
1982年 | 376篇 |
1981年 | 391篇 |
1980年 | 413篇 |
1979年 | 983篇 |
1978年 | 820篇 |
1977年 | 759篇 |
1976年 | 597篇 |
1975年 | 717篇 |
1974年 | 953篇 |
1973年 | 804篇 |
1972年 | 837篇 |
1971年 | 1046篇 |
1970年 | 1231篇 |
1969年 | 992篇 |
1968年 | 1005篇 |
1967年 | 927篇 |
1966年 | 786篇 |
1965年 | 613篇 |
1964年 | 229篇 |
1959年 | 340篇 |
1958年 | 600篇 |
1957年 | 454篇 |
1956年 | 371篇 |
1955年 | 362篇 |
1954年 | 366篇 |
1948年 | 273篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
74.
75.
J E Landegent N Jansen in de Wal G J van Ommen F Baas J J de Vijlder P van Duijn M Van der Ploeg 《Nature》1985,317(6033):175-177
During the past few years, several methods have been developed for the detection of specific nucleic acid sequences by in situ hybridization using non-radioactive labels such as fluorochromes, cytochemically detectable enzymes and electron-dense markers. These methods are preferable to autoradiography in terms of speed of performance and topological resolution. Their limited sensitivity, however, has so far restricted their use to the detection of repeated sequences. Here we report single gene detection with a procedure using 2-acetylaminofluorene (AAF)-modified probes, immunoperoxidase cytochemistry and reflection-contrast microscopy. We confirmed the autoradiographic data on the localization of the human thyroglobulin (Tg) gene to the distal end of the long arm of chromosome 8. A mixture of cosmid cHT2-derived subclones of the 3' part of the Tg gene, 22.3 kilobase pairs (kbp) in total, was used as a hybridization probe. This procedure can be used to map other unique sequences, if genomic clones are available from which clones with an appropriate amount of inserts can be isolated. 相似文献
76.
Yeo S H K Ramesh 《厦门大学学报(自然科学版)》2002,(Z1)
On going trend of miniaturization in electronic rel at ed parts, which is an average of two times in every 5~7 years introduce grindin g challenges. In grinding process, the surface waviness control of thin parts is an ardent task due to its warpage, induced by the high specific grinding energy (2~10 J/mm 3). Therefore, coolant is often used to avoid thermal damage, obtai n better surface integrity and to prolong wheel life. However coolant, the incomp ressibility media introduce high forces at the gri... 相似文献
77.
78.
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
79.
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
80.
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