全文获取类型
收费全文 | 9185篇 |
免费 | 937篇 |
国内免费 | 2篇 |
出版年
2023年 | 43篇 |
2021年 | 135篇 |
2020年 | 116篇 |
2019年 | 142篇 |
2018年 | 205篇 |
2017年 | 159篇 |
2016年 | 272篇 |
2015年 | 494篇 |
2014年 | 518篇 |
2013年 | 593篇 |
2012年 | 764篇 |
2011年 | 695篇 |
2010年 | 445篇 |
2009年 | 402篇 |
2008年 | 504篇 |
2007年 | 508篇 |
2006年 | 463篇 |
2005年 | 419篇 |
2004年 | 434篇 |
2003年 | 384篇 |
2002年 | 350篇 |
2001年 | 121篇 |
2000年 | 126篇 |
1999年 | 121篇 |
1998年 | 117篇 |
1997年 | 71篇 |
1996年 | 53篇 |
1995年 | 67篇 |
1994年 | 57篇 |
1993年 | 50篇 |
1992年 | 85篇 |
1991年 | 80篇 |
1990年 | 68篇 |
1989年 | 62篇 |
1988年 | 74篇 |
1987年 | 36篇 |
1986年 | 54篇 |
1985年 | 54篇 |
1984年 | 57篇 |
1983年 | 46篇 |
1982年 | 57篇 |
1981年 | 38篇 |
1980年 | 38篇 |
1979年 | 33篇 |
1978年 | 36篇 |
1977年 | 33篇 |
1976年 | 35篇 |
1974年 | 51篇 |
1973年 | 31篇 |
1972年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Anna-Kristina Marel Matthias Zorn Christoph Klingner Roland Wedlich-S?ldner Erwin Frey Joachim?O. R?dler 《Biophysical journal》2014,107(5):1054-1064
Collective migration of mechanically coupled cell layers is a notable feature of wound healing, embryonic development, and cancer progression. In confluent epithelial sheets, the dynamics have been found to be highly heterogeneous, exhibiting spontaneous formation of swirls, long-range correlations, and glass-like dynamic arrest as a function of cell density. In contrast, the flow-like properties of one-sided cell-sheet expansion in confining geometries are not well understood. Here, we studied the short- and long-term flow of Madin-Darby canine kidney (MDCK) cells as they moved through microchannels. Using single-cell tracking and particle image velocimetry (PIV), we found that a defined averaged stationary cell current emerged that exhibited a velocity gradient in the direction of migration and a plug-flow-like profile across the advancing sheet. The observed flow velocity can be decomposed into a constant term of directed cell migration and a diffusion-like contribution that increases with density gradient. The diffusive component is consistent with the cell-density profile and front propagation speed predicted by the Fisher-Kolmogorov equation. To connect diffusion-mediated transport to underlying cellular motility, we studied single-cell trajectories and occurrence of vorticity. We discovered that the directed large-scale cell flow altered fluctuations in cellular motion at short length scales: vorticity maps showed a reduced frequency of swirl formation in channel flow compared with resting sheets of equal cell density. Furthermore, under flow, single-cell trajectories showed persistent long-range, random-walk behavior superimposed on drift, whereas cells in resting tissue did not show significant displacements with respect to neighboring cells. Our work thus suggests that active cell migration manifests itself in an underlying, spatially uniform drift as well as in randomized bursts of short-range correlated motion that lead to a diffusion-mediated transport. 相似文献
2.
Daw-Yang Hwang Stefan Kohl Xueping Fan Asaf Vivante Stefanie Chan Gabriel C. Dworschak Julian Schulz Albertien M. van Eerde Alina C. Hilger Heon Yung Gee Tracie Pennimpede Bernhard G. Herrmann Glenn van de Hoek Kirsten Y. Renkema Christoph Schell Tobias B. Huber Heiko M. Reutter Neveen A. Soliman Natasa Stajic Radovan Bogdanovic Elijah O. Kehinde Richard P. Lifton Velibor Tasic Weining Lu Friedhelm Hildebrandt 《Human genetics》2015,134(8):905-916
3.
Maximilian Schmid Bianca Dufner Julius Dürk Konstanze Bedal Kristina Stricker Lukas Ali Prokoph Christoph Koch Anja K. Wege Henner Zirpel Ger van Zandbergen Rupert Ecker Bogdan Boghiu Uwe Ritter 《PloS one》2015,10(10)
Characterization of host-pathogen interactions is a fundamental approach in microbiological and immunological oriented disciplines. It is commonly accepted that host cells start to change their phenotype after engulfing pathogens. Techniques such as real time PCR or ELISA were used to characterize the genes encoding proteins that are associated either with pathogen elimination or immune escape mechanisms. Most of such studies were performed in vitro using primary host cells or cell lines. Consequently, the data generated with such approaches reflect the global RNA expression or protein amount recovered from all cells in culture. This is justified when all host cells harbor an equal amount of pathogens under experimental conditions. However, the uptake of pathogens by phagocytic cells is not synchronized. Consequently, there are host cells incorporating different amounts of pathogens that might result in distinct pathogen-induced protein biosynthesis. Therefore, we established a technique able to detect and quantify the number of pathogens in the corresponding host cells using immunofluorescence-based high throughput analysis. Paired with multicolor staining of molecules of interest it is now possible to analyze the infection profile of host cell populations and the corresponding phenotype of the host cells as a result of parasite load. 相似文献
4.
Christoph Plieth Burkhard Sattelmacher Ulf-Peter Hansen Marc R. Knight 《The Plant journal : for cell and molecular biology》1999,18(6):643-650
Aluminium, the most abundant metal in the earth's crust, is highly toxic to most plant species. One of the prevailing dogmas is that aluminium exerts this effect by disrupting cellular calcium homeostasis. However, recent research gives strongly conflicting results: aluminium was shown to provoke either an increase or a decrease in cytosolic free calcium concentration ([Ca2+]c). To solve this question, we have adopted a novel approach: [Ca2+]c measurements in intact plant roots as opposed to isolated cells, and the correlative measurements of intracellular and external pH. The results obtained show that plant roots respond to low external pH by a sustained elevation in [Ca2+]c. In the presence of aluminium, this pH-mediated elevation in [Ca2+]c does not occur, therefore any potential calcium-mediated protection against low pH is likely to be irreversibly inhibited. The severity of the inhibitory effect of aluminium on [Ca2+]c depends on the concentration of external calcium, thus perhaps explaining why the effects of aluminium toxicity are ameliorated in calcium-rich soils. It seems possible that a primary toxic effect of aluminium might be to impair calcium-mediated plant defence responses against low pH. 相似文献
5.
Seasonal changes of some water relations parameters of Norway spruce shoots ( Picea abies [L.] Karst.) were studied during two experiments using the pressure-volume analysis. For each experiment only shoots of a single tree were used.
During the first study, the course of the turgor loss point (as bulk osmotic pressure when turgor first reaches zero, πp) of shoots developed in late 1986 vegetation period, were measured in 1987. The turgor loss point decreased temporarily from –2.5 MPa at the beginning of the year to –3.3 MPa at the end of March, but then increased to the original level for the rest of the year.
During the second study, water relations parameters were measured in late summer 1987 and in late winter 1988. Winter shoots at full water saturation contained up to 20% less water than in late summer. Accordingly, the bulk osmotic pressure at full water saturation (πp ) decreased from –1.7 MPa in late summer to –1.9 MPa in winter, πp decreased also from –2.2 MPa to –2.8 MPa. However, the amount of osmotically active substances (mOsmol, N) remained unchanged. The relative amount of apoplastic water in the total shoot water content appeared to drop insignificantly from 17% to 15%.
The results show that the decrease in πo and πp in late winter is not due to an accumulation of osmotically active substances in the vacuoles but is due to a decrease in tissue water content. The temporary reduction of the symplastic volume by deposition of osmotically inert substances seems to be the most probable cause of this phenomenon. 相似文献
During the first study, the course of the turgor loss point (as bulk osmotic pressure when turgor first reaches zero, πp) of shoots developed in late 1986 vegetation period, were measured in 1987. The turgor loss point decreased temporarily from –2.5 MPa at the beginning of the year to –3.3 MPa at the end of March, but then increased to the original level for the rest of the year.
During the second study, water relations parameters were measured in late summer 1987 and in late winter 1988. Winter shoots at full water saturation contained up to 20% less water than in late summer. Accordingly, the bulk osmotic pressure at full water saturation (π
The results show that the decrease in π
6.
7.
8.
The cytomegalovirus enhancer: a pan-active control element in transgenic mice. 总被引:41,自引:2,他引:39 下载免费PDF全文
In an effort to identify widely active positive regulatory elements, we have examined the action of the cytomegalovirus enhancer-promoter in transgenic mice. These elements activated expression in 24 of 28 tissues tested. The greatest expression was observed in the heart, kidney, brain, and testis. Maximum expression further localized to specific cells within the heart and kidney. 相似文献
9.
10.