全文获取类型
收费全文 | 760篇 |
免费 | 114篇 |
国内免费 | 2篇 |
出版年
2022年 | 4篇 |
2021年 | 20篇 |
2020年 | 9篇 |
2019年 | 14篇 |
2018年 | 9篇 |
2017年 | 7篇 |
2016年 | 15篇 |
2015年 | 21篇 |
2014年 | 32篇 |
2013年 | 39篇 |
2012年 | 56篇 |
2011年 | 53篇 |
2010年 | 33篇 |
2009年 | 30篇 |
2008年 | 37篇 |
2007年 | 38篇 |
2006年 | 34篇 |
2005年 | 40篇 |
2004年 | 40篇 |
2003年 | 26篇 |
2002年 | 36篇 |
2001年 | 17篇 |
2000年 | 15篇 |
1999年 | 30篇 |
1998年 | 15篇 |
1997年 | 8篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 8篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1979年 | 5篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1969年 | 5篇 |
1967年 | 2篇 |
1966年 | 3篇 |
排序方式: 共有876条查询结果,搜索用时 687 毫秒
301.
302.
Addington RN Donovan LA Mitchell RJ Vose JM Pecot SD Jack SB Hacke UG Sperry JS Oren R 《Plant, cell & environment》2006,29(4):535-545
We investigated relationships between whole-tree hydraulic architecture and stomatal conductance in Pinus palustris Mill. (longleaf pine) across habitats that differed in soil properties and habitat structure. Trees occupying a xeric habitat (characterized by sandy, well-drained soils, higher nitrogen availability and lower overstory tree density) were shorter in stature and had lower sapwood-to-leaf area ratio (A(S):A(L)) than trees in a mesic habitat. The soil-leaf water potential gradient (psiS - psiL) and leaf-specific hydraulic conductance (kL) were similar between sites, as was tissue-specific hydraulic conductivity (Ks) of roots. Leaf and canopy stomatal conductance (gs and Gs, respectively) were also similar between sites, and they tended to be somewhat higher at the xeric site during morning hours when vapour pressure deficit (D) was low. A hydraulic model incorporating tree height, A(S):A(L) and psiS-psiL accurately described the observed variation in individual tree G(Sref) (G(S) at D = 1 kPa) across sites and indicated that tree height was an important determinant of G(Sref) across sites. This, combined with a 42% higher root-to-leaf area ratio (A(R):A(L)) at the xeric site, suggests that xeric site trees are hydraulically well equipped to realize equal--and sometimes higher potential for conductance compared with trees on mesic sites. However, a slightly more sensitive stomatal closure response to increasing D observed in xeric site trees suggests that this potential for higher conductance may only be reached when D is low and when the capacity of the hydraulic system to supply water to foliage is not greatly challenged. 相似文献
303.
Host responses influence on the induction of lambda prophage 总被引:1,自引:0,他引:1
Rokney A Kobiler O Amir A Court DL Stavans J Adhya S Oppenheim AB 《Molecular microbiology》2008,68(1):29-36
304.
Longfei Chen Yingying Li Qian Zhang Oren Akhberdi Dongsheng Wei Jiao Pan Xudong Zhu 《Mycoscience》2017,58(1):35-39
To reduce the unnecessary gene clusters in the taxol-producing fungus Pestalotiopsis microspora, we report the development of an effective DNA deletion method that relies on a deletion cassette constructed with the Gateway-technique and overlap extension PCR, using the orotidine 5′-phosphate decarboxylase as recyclable marker for selection. By this approach, two adjacent DNA sequences can be sequentially deleted in a single transformation mediated by Agrobacterium tumefaciens, resulting in the deletion of a large DNA fragment. Additionally, the selection marker is spontaneously eliminated in this process. We used this method to successfully remove the mus53 locus of P. microspora. 相似文献
305.
Daniel B. Metcalfe Daniel Ricciuto Sari Palmroth Catherine Campbell Vaughan Hurry Jiafu Mao Sonja G. Keel Sune Linder Xiaoying Shi Torgny Näsholm Klas E. A. Ohlsson M. Blackburn Peter E. Thornton Ram Oren 《Global Change Biology》2017,23(5):2130-2139
Models predicting ecosystem carbon dioxide (CO2) exchange under future climate change rely on relatively few real‐world tests of their assumptions and outputs. Here, we demonstrate a rapid and cost‐effective method to estimate CO2 exchange from intact vegetation patches under varying atmospheric CO2 concentrations. We find that net ecosystem CO2 uptake (NEE) in a boreal forest rose linearly by 4.7 ± 0.2% of the current ambient rate for every 10 ppm CO2 increase, with no detectable influence of foliar biomass, season, or nitrogen (N) fertilization. The lack of any clear short‐term NEE response to fertilization in such an N‐limited system is inconsistent with the instantaneous downregulation of photosynthesis formalized in many global models. Incorporating an alternative mechanism with considerable empirical support – diversion of excess carbon to storage compounds – into an existing earth system model brings the model output into closer agreement with our field measurements. A global simulation incorporating this modified model reduces a long‐standing mismatch between the modeled and observed seasonal amplitude of atmospheric CO2. Wider application of this chamber approach would provide critical data needed to further improve modeled projections of biosphere–atmosphere CO2 exchange in a changing climate. 相似文献
306.
Hydrologic balance in an intact temperate forest ecosystem under ambient and elevated atmospheric CO2 concentration 总被引:1,自引:0,他引:1
Abstract Increasing atmospheric CO2 concentration decreases stomatal conductance in many species, but the savings of water from reduced transpiration may permit the forest to retain greater leaf area index (L). Therefore, the net effect on water use in forest ecosystems under a higher CO2 atmosphere is difficult to predict. The free air CO2 enrichment (FACE) facility (n = 3) in a 14‐m tall (in 1996) Pinus taeda L. stand was designed to reduce uncertainties in predicting such responses. Continuous measurements of precipitation, throughfall precipitation, sap flux, and soil moisture were made over 3.5 years under ambient (CO2a) and elevated (CO2e) ambient + 200 µmol mol?1). Annual stand transpiration under ambient CO2 conditions accounted for 84–96% of latent heat flux measured with the eddy‐covariance technique above the canopy. Under CO2e, P. taeda transpired less per unit of leaf area only when soil drought was severe. Liquidambar styraciflua, the other major species in the forest, used progressively less water, settling at 25% reduction in sap flux density after 3.5 years under CO2e. Because P. taeda dominated the stand, and severe drought periods were of relatively short duration, the direct impact of CO2e on water savings in the stand was undetectable. Moreover, the forest used progressively more water under CO2e, probably because soil moisture availability progressively increased, probably owing to a reduction in soil evaporation caused by more litter buildup in the CO2e plots. The results suggest that, in this forest, the effect of CO2e on transpiration was greater indirectly through enhanced litter production than directly through reduced stomatal conductance. In forests composed of species more similar to L. styraciflua, water savings from stomatal closure may dominate the response to CO2e. 相似文献
307.
Thermophilic and halophilic extremophiles. 总被引:6,自引:0,他引:6
The microbiology of extremely hot or saline habitats is a fast moving field with many new successes in the enrichment and isolation of new organisms and in an understanding of molecular factors that impart stability on thermostable and halophilic biomolecules. The results of these studies have shed new light on our understanding of prokaryotic diversity and structural biochemistry. 相似文献
308.
Excess beta-catenin promotes accumulation of transcriptionally active p53. 总被引:11,自引:0,他引:11
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A Damalas A Ben-Ze''ev I Simcha M Shtutman J F Leal J Zhurinsky B Geiger M Oren 《The EMBO journal》1999,18(11):3054-3063
309.
Co-operation between the p53 protein tumor antigen and platelet-poor plasma in the induction of cellular DNA synthesis 总被引:9,自引:0,他引:9
Plasmids containing DNA sequences coding for p53 were microinjected into quiescent Swiss 3T3 cells. Three constructs were used, carrying either the whole gene sequence, a full-length cDNA, or a hybrid between the gene and the cDNA. All of them stimulated DNA synthesis when cells were incubated with platelet-poor plasma (PPP) following injection. The p53 gene stimulated DNA synthesis to a lesser extent, also in the absence of PPP. Several negative results were obtained with different plasmids, including deletion mutants in the p53 coding region. However, a deletion mutant in which the p53 reading frame ended in the middle of the coding part of the p53 gene still stimulated DNA synthesis in co-operation with PPP. The stimulation of DNA synthesis induced by p53 cDNA was more synchronous and more limited than that induced by serum. The present data suggest that p53 may act as a competence factor in cell cycle progression. 相似文献
310.
The light-activated channels of Drosophila photoreceptors transient receptor potential (TRP) and TRP-like (TRPL) show voltage-dependent conductance during illumination. Recent studies implied that mammalian members of the TRP family, which belong to the TRPV and TRPM subfamilies, are intrinsically voltage-gated channels. However, it is unclear whether the Drosophila TRPs, which belong to the TRPC subfamily, share the same voltage-dependent gating mechanism. Exploring the voltage dependence of Drosophila TRPL expressed in S2 cells, we found that the voltage dependence of this channel is not an intrinsic property since it became linear upon removal of divalent cations. We further found that Ca(2+) blocked TRPL in a voltage-dependent manner by an open channel block mechanism, which determines the frequency of channel openings and constitutes the sole parameter that underlies its voltage dependence. Whole cell recordings from a Drosophila mutant expressing only TRPL indicated that Ca(2+) block also accounts for the voltage dependence of the native TRPL channels. The open channel block by Ca(2+) that we characterized is a useful mechanism to improve the signal to noise ratio of the response to intense light when virtually all the large conductance TRPL channels are blocked and only the low conductance TRP channels with lower Ca(2+) affinity are active. 相似文献