全文获取类型
收费全文 | 9072篇 |
免费 | 482篇 |
国内免费 | 1篇 |
专业分类
9555篇 |
出版年
2023年 | 41篇 |
2022年 | 51篇 |
2021年 | 120篇 |
2020年 | 121篇 |
2019年 | 152篇 |
2018年 | 312篇 |
2017年 | 276篇 |
2016年 | 386篇 |
2015年 | 319篇 |
2014年 | 421篇 |
2013年 | 641篇 |
2012年 | 518篇 |
2011年 | 679篇 |
2010年 | 405篇 |
2009年 | 298篇 |
2008年 | 502篇 |
2007年 | 570篇 |
2006年 | 594篇 |
2005年 | 505篇 |
2004年 | 412篇 |
2003年 | 474篇 |
2002年 | 391篇 |
2001年 | 208篇 |
2000年 | 172篇 |
1999年 | 126篇 |
1998年 | 84篇 |
1997年 | 33篇 |
1996年 | 26篇 |
1995年 | 34篇 |
1994年 | 24篇 |
1993年 | 22篇 |
1992年 | 21篇 |
1991年 | 32篇 |
1990年 | 26篇 |
1989年 | 25篇 |
1988年 | 18篇 |
1987年 | 23篇 |
1986年 | 26篇 |
1985年 | 38篇 |
1984年 | 28篇 |
1983年 | 19篇 |
1982年 | 25篇 |
1981年 | 23篇 |
1980年 | 19篇 |
1979年 | 24篇 |
1978年 | 25篇 |
1977年 | 22篇 |
1976年 | 15篇 |
1953年 | 19篇 |
1952年 | 40篇 |
排序方式: 共有9555条查询结果,搜索用时 11 毫秒
1.
2.
Daniël C. Koppenol Fred J. Vermolen 《Biomechanics and modeling in mechanobiology》2017,16(4):1187-1206
A continuum hypothesis-based model is developed for the simulation of the (long term) contraction of skin grafts that cover excised burns in order to obtain suggestions regarding the ideal length of splinting therapy and when to start with this therapy such that the therapy is effective optimally. Tissue is modeled as an isotropic, heterogeneous, morphoelastic solid. With respect to the constituents of the tissue, we selected the following constituents as primary model components: fibroblasts, myofibroblasts, collagen molecules, and a generic signaling molecule. Good agreement is demonstrated with respect to the evolution over time of the surface area of unmeshed skin grafts that cover excised burns between outcomes of computer simulations obtained in this study and scar assessment data gathered previously in a clinical study. Based on the simulation results, we suggest that the optimal point in time to start with splinting therapy is directly after placement of the skin graft on its recipient bed. Furthermore, we suggest that it is desirable to continue with splinting therapy until the concentration of the signaling molecules in the grafted area has become negligible such that the formation of contractures can be prevented. We conclude this study with a presentation of some alternative ideas on how to diminish the degree of contracture formation that are not based on a mechanical intervention, and a discussion about how the presented model can be adjusted. 相似文献
3.
Rafał Krętowski Anna Stypułkowska Marzanna Cechowska-Pasko 《Molecular and cellular biochemistry》2015,398(1-2):165-173
The inhibition of the 26S proteasome evokes endoplasmic reticulum stress, which has been shown to be implicated in the antitumoral effects of proteasome inhibitors. The cellular and molecular effects of the proteasome inhibitor—bortezomib—on human colon cancer cells are as yet poorly characterized. Bortezomib selectively induces apoptosis in some cancer cells. However, the nature of its selectivity remains unknown. Previously, we demonstrated that, in contrast to normal fibroblasts, bortezomib treatment evoked strong effect on apoptosis of breast cancer cells incubated in hypoxic and normoxic conditions. The study presented here provides novel information on the cellular effects of bortezomib in DLD-1 colon cancer cells line. We observe twofold higher percentage of apoptotic cells incubated for 48 h with 25 and 50 nmol/l of bortezomib in hypoxic conditions and four-, fivefold increase in normoxic conditions in comparison to control cells, incubated without bortezomib. It is of interest that bortezomib evokes strong effect on necrosis of DLD-1 colon cancer cell line. We observe the sixfold increase in necrosis of DLD-1 cells incubated with 25 or 50 nmol/l of bortezomib for 48 h in hypoxia and fourfold increase in normoxic conditions in comparison to adequate controls. We suggest that bortezomib may be candidates for further evaluation as chemotherapeutic agents for human colon cancer. 相似文献
4.
Distinct effects of climate warming on populations of silver fir (Abies alba) across Europe
下载免费PDF全文
![点击此处可从《Journal of Biogeography》网站下载免费的PDF全文](/ch/ext_images/free.gif)
5.
6.
Jacek Kęsy Beata Maciejewska Magdalena Sowa Magdalena Szumilak Krzysztof Kawałowski Maja Borzuchowska Jan Kopcewicz 《Plant Growth Regulation》2008,55(1):43-50
It has been shown that both IAA and ethylene application inhibit flower induction in the short-day plant Pharbitis nil. However application of IAA has elevated ethylene production in this plant, as well. Strong enhancement of ethylene production
is also correlated with the night-break effect, which completely inhibits flowering. In order to determine what the role of
IAA and ethylene is in the photoperiodic flower induction in Pharbitis nil, we measured changes in their levels during inductive and non-inductive photoperiods, and the effects of ethylene biosynthesis
and action inhibitors on inhibition of flowering by IAA. Our results have shown that the inhibitory effect of IAA on Pharbitis nil flowering is not physiological but is connected with its effect on ethylene biosynthesis. 相似文献
7.
T. Cichocki B. Gonsior J. Glazur M. Höfert L. Jarczyk E. Rokita A. Strzałkowski M. Sych 《Biological trace element research》1987,13(1):167-177
The elemental composition of rabbit liver was determined by the PIXE and micro-PIXE methods. The mean concentrations of P,
S, Cl, K, Fe, Cu, Zn, and Rb measured by both methods were similar. The latter method also allowed for localization of elements
within lobule territory. It has been found that some elements are more prevalent in the veins (Cl, Fe) and others in the liver
parenchyma (P, Cu, Zn). Moreover, Zn showed the characteristic intralobular distribution. Some methodological aspects of microbeam
application to biological materials were also discussed. 相似文献
8.
Monovalent and divalent cation permeation in acetylcholine receptor channels. Ion transport related to structure 总被引:14,自引:4,他引:10
下载免费PDF全文
![点击此处可从《The Journal of general physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Single channel patch-clamp techniques were used to study nicotinic acetylcholine receptors in cultured rat myotubes. The single channel conductance in pure cesium and sodium levels off at high concentrations, as if a binding site within the channel were saturating. The conductances at very low concentrations, however, are larger than predicted by the simplest one-site transport model fitted to the high-concentration data. At low concentrations, the current-voltage relations are inwardly rectifying, but they become more ohmic if a small amount of divalent cations is added externally. Magnesium and barium are good permeants that have rather high affinities for the channel. Upon adding low millimolar concentrations of these divalent cations externally to a membrane bathed in pure cesium, the inward current carried by cesium is decreased. As more divalent cations are added, the inward-going currents continued to decrease and the divalent cation replaces cesium as the main current carrier. The ion transport data are described by considering the size, shape, and possible net charge of the channel. In that way, even the complex features of transport are explained in a realistic physical framework. The results are consistent with the channel having long, wide, multiply occupied vestibules that serve as transition zones to the short, selective, singly occupied narrow region of the channel. A small amount of net negative charge within the pore could produce concentration-dependent potentials that provide a simple explanation for the more complicated aspects of the permeation properties. 相似文献
9.
R. G. Dani R. J. Kohel 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,77(4):569-575
Summary The nature of gene action and of maternal influence governing cottonseed oil attributes were determined with four lines, two each with high and low seed-oil percentage. For this purpose, P1, P2, F0, F1, F2 and alternative sets of BC1 and BC2 generations were analysed in six cross-combinations and their reciprocals. Marginal extents of heterosis for seed-oil percentage were noticeable in F1, with inbreeding depression in F2. Data from reciprocal backcrosses provided evidence in favour of maternal rather than cytoplasmic effects of seed-oil development. Relatively higher extents of heterosis, sizeable inbreeding depression and reciprocally unequal F2 averages were characteristic of the seed index trait, which often showed a reversal of effects from F1 to F2. Reverse reciprocal backcrosses exhibited some differences, including greater resemblance between the types, (A/B)A and (B/A)A, in addition to variable dose effects in seed index. Thus, the differences between F1 seed index values were not due to cytoplasmic influence. Positive heterotic effects for seed-oil index, especially among the backcrosses, ranged between 16.08% and 47.29% over midparent averages. Genetic component estimates from analysis of similar sets of crosses differing only in reciprocal backcrosses, and also from sets of reciprocal crosses between any two parental combinations, were inconsistent. Scaling tests detected presence of epistasis within and between a majority of cross-combinations. Despite reciprocal differences, additive gene effects for seed-oil percentage were significant in 7 out of 24 crosses, representing high x low, low x high and low x low seed-oil parents. Those were, however, accompanied by significant dominance effects of higher order. In crosses involving low seed-oil percentage parents SA1060 and SA229, all six components were detected significant, with opposite effects of dominance and dominance x dominance epistatic components. Significant additive components were also detected for seed index and seed-oil index in 7 and 5 out of 24 crosses, respectively. In the inheritance of seed index and seed-oil index, dominance effects were more important. Epistatic components of additive x additive, and to a lesser extent, those of dominant x dominant were found significant. 相似文献
10.
A simple procedure is described for the determination of the photosensitizing potency of drugs, using three leukemic cell lines, two of lymphocytic origin, L1210 and P388 and one of erythroid type, Friend-745. The procedure allows one to investigate several aspects of the photosensitization properties of tested compounds such as cellular localization and direct (trypan blue exclusion) or delayed (clonogenicity) photomediated toxicities.The method was assessed using crude hematoporphyrin derivative (HPD) as well as dihematoporphyrin ether (DHE) or commercially available Photofrin II. Results were compared to those obtained with normal cells, e.g spleen lymphocytes and erythropoietic stem cells (CFU-e), and discussed in the light of the relative response of normal versus transformed cells.Abbreviations DHE
Dihematoporphyrin Ether
- FCS
Fetal Calf Serum
- HPD
Hematoporphyrin Derivative
- PDT
Photodynamic Therapy 相似文献