全文获取类型
收费全文 | 6034篇 |
免费 | 564篇 |
国内免费 | 3篇 |
专业分类
6601篇 |
出版年
2022年 | 54篇 |
2021年 | 117篇 |
2020年 | 63篇 |
2019年 | 67篇 |
2018年 | 78篇 |
2017年 | 60篇 |
2016年 | 134篇 |
2015年 | 266篇 |
2014年 | 262篇 |
2013年 | 388篇 |
2012年 | 484篇 |
2011年 | 441篇 |
2010年 | 258篇 |
2009年 | 210篇 |
2008年 | 372篇 |
2007年 | 384篇 |
2006年 | 322篇 |
2005年 | 275篇 |
2004年 | 280篇 |
2003年 | 275篇 |
2002年 | 276篇 |
2001年 | 68篇 |
2000年 | 42篇 |
1999年 | 57篇 |
1998年 | 86篇 |
1997年 | 53篇 |
1996年 | 50篇 |
1995年 | 40篇 |
1994年 | 54篇 |
1993年 | 43篇 |
1992年 | 35篇 |
1991年 | 31篇 |
1990年 | 43篇 |
1989年 | 34篇 |
1988年 | 33篇 |
1986年 | 29篇 |
1985年 | 38篇 |
1984年 | 37篇 |
1983年 | 41篇 |
1982年 | 42篇 |
1981年 | 42篇 |
1980年 | 33篇 |
1978年 | 27篇 |
1977年 | 25篇 |
1976年 | 33篇 |
1975年 | 29篇 |
1974年 | 28篇 |
1973年 | 27篇 |
1972年 | 24篇 |
1969年 | 25篇 |
排序方式: 共有6601条查询结果,搜索用时 0 毫秒
151.
Ruth Graf Monika Meyer-Holzapfel 《Ethology : formerly Zeitschrift fur Tierpsychologie》1974,35(3):320-332
An 11 Versuchstagen wurden die Reaktionen von insgesamt 3 Rüden und 2 Hündinnen auf einem rund 2stündigen Spaziergang in nicht oder wenig bekanntem Gebiet beobachtet. Auf einem ersten Rundgang wurden die spontan abgegebenen Harnmarken eines Versuchstieres mit kleinen Objekten markiert, dann ein zweiter Hund an loser Leine den gleichen Weg (meist in umgekehrter Richtung) entlanggeführt und dessen Reaktionen auf die markierten Stellen registriert. Im ganzen wurden bei den ersten Rundgängen 261 Harnmarken abgesetzt. In 47,1 % der Fälle ging der im zweiten Rundgang vorbeigeführte Hund ohne ersichtlichen Grund an der Harnmarke vorbei. Bei Beachtung der Marken zeigten sich 6 verschiedene Reaktionen: 1. Beschnuppern, 2. Harnen über oder neben die Marke, 3. Scharren mit den Hinterpfoten nach Überharnen, 4. Belecken der Marke, 5. Knurren beim Scharren, 6. Zähneklappern nach Beschnuppern und Belecken. Die Marken von feindlichen Rüden und läufigen Hündinnen werden nach Beschnuppern signifikant häufiger als die eigenen bzw. diejenigen einer nichtläufigen Hündin mit einer weiteren Reaktion beantwortet. Die Marken nichtläufiger Hündinnen und die eigenen Marken ergaben keine unterschiedlichen Reaktionen beim Rüden. Eine Hündin reagiert auf die Marken eines (feindl.) Rüden nicht mehr als ein Rüde auf die eigenen Marken. Die Harnmarken vermitteln dem Hunderüden Informationen darüber, ob sie von einer läufigen Hündin, einem fremden Rüden oder von ihm selbst (bzw. einer nicht-läufigen Hündin) stammen. 相似文献
152.
Cell migration and growth are essential components of the development of multicellular organisms. The role of various cues
in directing cell migration is widespread, in particular, the role of signals in the environment in the control of cell motility
and directional guidance. In many cases, especially in developmental biology, growth of the domain also plays a large role
in the distribution of cells and, in some cases, cell or signal distribution may actually drive domain growth. There is an
almost ubiquitous use of partial differential equations (PDEs) for modelling the time evolution of cellular density and environmental
cues. In the last 20 years, a lot of attention has been devoted to connecting macroscopic PDEs with more detailed microscopic
models of cellular motility, including models of directional sensing and signal transduction pathways. However, domain growth
is largely omitted in the literature. In this paper, individual-based models describing cell movement and domain growth are
studied, and correspondence with a macroscopic-level PDE describing the evolution of cell density is demonstrated. The individual-based
models are formulated in terms of random walkers on a lattice. Domain growth provides an extra mathematical challenge by making
the lattice size variable over time. A reaction–diffusion master equation formalism is generalised to the case of growing
lattices and used in the derivation of the macroscopic PDEs. 相似文献
153.
154.
155.
Structure and properties of rat thymus deoxyribonucleoprotein. Solubility properties and effects of precipitation 总被引:2,自引:1,他引:1
Ruth F. Itzhaki 《The Biochemical journal》1967,105(2):741-748
1. Deoxyribonucleoprotein was prepared from rat thymus and was studied chiefly by the method of electric birefringence. The birefringence depends on the electrical and optical properties of the molecules and on their volume; the decay time of birefringence (after the removal of the electric field) depends on molecular length. 2. A comparison was made of the properties of deoxyribonucleoprotein redissolved after precipitation in 0.15m-sodium chloride with those of the original material, the main object being to find if structural changes have occurred in the former. As a preliminary, the dependence of the solubility of the deoxyribonucleoprotein on the concentration of added salt was investigated, and the birefringence properties were also studied after the addition of sodium chloride at low concentrations, after the alteration of pH and after dialysis. 3. It was found that precipitation of deoxyribonucleoprotein occurs in two fractions, beginning at about 0.4mm-sodium chloride. The solubility is minimal at about 0.15m-sodium chloride. 4. The electric birefringence and decay time of the deoxyribonucleoprotein decrease with increasing concentration of added sodium chloride, and the birefringence also decreases after dialysis. Prolonged dialysis leads to precipitation. 5. The properties of deoxyribonucleoprotein redissolved after precipitation with 0.15m-sodium chloride differ considerably from those of the original deoxyribonucleoprotein. This is attributed to some type of disorganization process occurring during precipitation. It is concluded that the organization of the original structure is very specific. 相似文献
156.
157.
158.
Abstract Three well-defined E. coli operator regions were examined for recurring conformational deviation from a regular B-DNA helix. All three, the lac, trp, and gal, show repeats of the same set of neighboring helical twist angles. These angles recur with a periodicity equal to the helix periodicity on one side of the operator's axes of symmetry. The probability that their occurrence is random was found to be extremely small. Therefore, we propose that in addition to specific bases, repeating twist angle patterns are likely to be among the local parameters involved in repressor-operator recognition. 相似文献
159.
160.
Loree Heller Reynald Thinard Melanie Chevalier Sezgi Arpag Yu Jing Ruth Greferath Richard Heller Claude Nicolau 《Journal of cellular and molecular medicine》2020,24(15):8772-8778
In neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, multiple sclerosis and amyotrophic lateral sclerosis, neuroinflammation can lead to blood‐brain barrier (BBB) breakdown. After intravenous or intra‐arterial injection into mice, endothelial progenitor cells (EPCs) home to the damaged BBB to promote neurovascular repair. Autologous EPCs transfected to express specific therapeutic proteins offer an innovative therapeutic option. Here, we demonstrate that EPC transfection by electroporation with plasmids encoding the reporter protein GFP or an anti‐β‐amyloid antibody fragment (Fab) leads to secretion of each protein. We also demonstrate the secreted anti‐β‐amyloid Fab protein functions in β‐amyloid aggregate solubilization. 相似文献