全文获取类型
收费全文 | 8275篇 |
免费 | 666篇 |
国内免费 | 12篇 |
出版年
2023年 | 45篇 |
2022年 | 33篇 |
2021年 | 175篇 |
2020年 | 123篇 |
2019年 | 146篇 |
2018年 | 196篇 |
2017年 | 164篇 |
2016年 | 251篇 |
2015年 | 394篇 |
2014年 | 431篇 |
2013年 | 565篇 |
2012年 | 659篇 |
2011年 | 561篇 |
2010年 | 407篇 |
2009年 | 336篇 |
2008年 | 458篇 |
2007年 | 437篇 |
2006年 | 414篇 |
2005年 | 357篇 |
2004年 | 343篇 |
2003年 | 299篇 |
2002年 | 271篇 |
2001年 | 153篇 |
2000年 | 160篇 |
1999年 | 131篇 |
1998年 | 60篇 |
1997年 | 53篇 |
1996年 | 56篇 |
1995年 | 57篇 |
1994年 | 55篇 |
1993年 | 52篇 |
1992年 | 87篇 |
1991年 | 79篇 |
1990年 | 72篇 |
1989年 | 62篇 |
1988年 | 56篇 |
1987年 | 44篇 |
1986年 | 61篇 |
1985年 | 49篇 |
1984年 | 49篇 |
1983年 | 35篇 |
1979年 | 36篇 |
1978年 | 28篇 |
1977年 | 30篇 |
1976年 | 24篇 |
1972年 | 24篇 |
1970年 | 30篇 |
1969年 | 34篇 |
1968年 | 29篇 |
1965年 | 23篇 |
排序方式: 共有8953条查询结果,搜索用时 15 毫秒
1.
2.
3.
Sequence complexity and diversity of polyadenylated RNA molecules transcribed in human myeloid cells
4.
Amy Chapman Gonzalo Gonzales Wayne R. Burrowes Paul Assanah Bernadette Iannone Michael K. Leung George B. Stefano 《Cellular and molecular neurobiology》1984,4(2):143-155
In Mytilus and Leucophaea the high-affinity binding site density is significantly lower in old animals than in young animals, whereas the low-affinity site density remains unchanged. In Mytilus the estimated met-enkephalin and met-enkephalin-Arg6-Phe7 levels are significantly higher in old than in young animals. In Leucophaea only the met-enkephalin level can be determined, and it is also higher in old animals. The decrease in the high-affinity binding site density and the corresponding increase in endogenous enkephalin levels suggest the existence of an opioid compensatory mechanism associated with the aging process. In Mytilus there is a demonstrated decrease with age in intraganglionic dopamine levels in response to applied opiates. In addition, the inhibition of dopamine-stimulated adenylate cyclase activity by opiates also decreases in older animals. In Leucophaea the sex difference in opioid binding densities diminishes with age. 相似文献
5.
Differential and integral W-values for ionization in gaseous water for electron and proton irradiation have been analyzed from the theoretical point of view for consistency between ionization and total inelastic collision cross sections. For low-energy electrons, which are ubiquitous for all primary radiations, the experimental or compiled cross sections from different sources are sometimes not consistent with one another. A practical, self-consistent procedure is outlined in such cases. The high-energy asymptotic W-values for differential and integral ionization are calculated to be 33.7 and 34.7 eV, respectively, for electron irradiation and 34.6 and 32.5 eV, respectively, for proton irradiation. The computed variations of the W-values with energy are generally in good agreement with experiment. Integral primary W-values due only to the interactions between the incident particle and the water vapor are calculated to be 43.5 and 45.0 eV for electrons and protons, respectively, in the high-energy asymptotic limit. 相似文献
6.
7.
Summary Pollen mother cells at early meiotic prophase fromFritillaria lanceolata, F. mutica, Tulbaghia violacea, the lily “Formobel”,Triticum aegilopoides, T. dicoccoides, T. aestivum and synaptic and asynaptic forms ofT. durum were studied in thin sections with the electron microscope (a) in relation to distribution of nuclear pores (b) in respect
of fine structure of the pore complex in those of the first four. The pores were distributed in random clusters during leptotene
to pachytene in all plants, except in the two forms ofT. durum where there were either no pores or so few that they were not detectable. Probably correlated with this, the two membranes
of the nuclear envelope were often widely separated and frequently sacculated. No pores were seen at leptotene in the part
of the envelope to which, in theFritillarias and lily, the nucleolus was adpressed at this time. Evidence supporting a recent model which proposes that annuli are composed
of three rings of eight granular subunits was obtained. These subunits as well as a dense central element, observed in most
pores, were composed of filaments about 3 nm in diameter and evidently protein in character. There was evidence of a continuity
between filaments in the central element and those in the rings of subunits which encircle the pore aperture at both the nuclear
and cytoplasmic sides of the pore. In profiles of pores knobbed filaments were sometimes seen extending laterally from the
pore wall into the perinuclear space at two sides. Questions concerning the role of the annulus are discussed.
The author wish to thank Mr. R. F. Scott for construction to the model. 相似文献
8.
9.
10.