全文获取类型
收费全文 | 1220篇 |
免费 | 128篇 |
出版年
2019年 | 11篇 |
2018年 | 9篇 |
2016年 | 12篇 |
2015年 | 29篇 |
2014年 | 31篇 |
2013年 | 44篇 |
2012年 | 51篇 |
2011年 | 45篇 |
2010年 | 35篇 |
2009年 | 40篇 |
2008年 | 38篇 |
2007年 | 47篇 |
2006年 | 45篇 |
2005年 | 40篇 |
2004年 | 38篇 |
2003年 | 42篇 |
2002年 | 47篇 |
2001年 | 39篇 |
2000年 | 39篇 |
1999年 | 29篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 12篇 |
1993年 | 10篇 |
1992年 | 27篇 |
1991年 | 23篇 |
1990年 | 24篇 |
1989年 | 26篇 |
1988年 | 19篇 |
1987年 | 19篇 |
1986年 | 28篇 |
1985年 | 19篇 |
1984年 | 29篇 |
1983年 | 17篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 20篇 |
1979年 | 36篇 |
1978年 | 20篇 |
1977年 | 12篇 |
1976年 | 19篇 |
1975年 | 15篇 |
1974年 | 21篇 |
1973年 | 17篇 |
1972年 | 13篇 |
1971年 | 11篇 |
1969年 | 16篇 |
1968年 | 15篇 |
1967年 | 15篇 |
1966年 | 13篇 |
排序方式: 共有1348条查询结果,搜索用时 15 毫秒
61.
Hydrobiologia - After publication of the above mentioned article, previously undisclosed material was made available resulting in an altered population status for the below mentioned species: 相似文献
62.
63.
Rajesh Mohandas Larysa Sautina Shiyu Li Xuerong Wen Tianyao Huo Eileen Handberg Yueh-Yun Chi C. Noel Bairey Merz Carl J. Pepine Mark S. Segal 《PloS one》2013,8(12)
Background
In women with ischemia and no obstructive coronary artery disease, the Women''s Ischemic Syndrome Evaluation (WISE) observed that microvascular coronary dysfunction (MCD) is the best independent predictor of adverse cardiovascular events. Since coronary microvascular tone is regulated in part by endothelium, we hypothesized that circulating endothelial cells (CEC), which reflect endothelial injury, and the number and function of bone-marrow derived angiogenic cells (BMDAC), which could help repair damaged endothelium, may serve as biomarkers for decreased coronary flow reserve (CFR) and MCD.Methods
We studied 32 women from the WISE cohort. CFR measurements in response to intracoronary adenosine were taken as an index of MCD. We enumerated BMDAC colonies and CEC in peripheral blood samples. BMDAC function was assessed by assay of migration of CD34+ cells toward SDF-1 and measurement of bioavailable nitric oxide (NO). These findings were compared with a healthy reference group and also entered into a multivariable model with CFR as the dependent variable.Results
Compared with a healthy reference group, women with MCD had lower numbers of BMDAC colonies [16 (0, 81) vs. 24 (14, 88); P = 0.01] and NO [936 (156, 1875) vs. 1168 (668, 1823); P = 0.02]. Multivariable regression analysis showed strong correlation of CFR to the combination of BMDAC colony count and CD34+ cell function (migration and NO) (R2 = 0.45; P<0.05).Conclusions
The BMDAC function and numbers of BMDAC colonies are decreased in symptomatic women with MCD and are independently associated with CFR. These circulating cells may provide mechanistic insights into MCD in women with ischemia. 相似文献64.
Daniela Jerszurki Or Sperling Theivasigamani Parthasarathi Juliana Espada Lichston Adi Yaaran Menachem Moshelion Shimon Rachmilevitch Naftali Lazarovitch 《Physiologia plantarum》2020,170(1):60-74
Plants optimize water use and carbon assimilation via transient regulation of stomata resistance and by limiting hydraulic conductivity in a long-term response of xylem anatomy. We postulated that without effective hydraulic regulation plants would permanently restrain water loss and photosynthetic productivity under salt stress conditions. We compared wild-type tomatoes to a transgenic type (TT) with impaired stomatal control. Gas exchange activity, biomass, starch content, leaf area and root traits, mineral composition and main stems xylem anatomy and hydraulic conductivity were analyzed in plants exposed to salinities of 1 and 4 dS m−1 over 60 days. As the xylem cannot easily readjust to different environmental conditions, shifts in its anatomy and the permanent effect on plant hydraulic conductivity kept transpiration at lower levels under unstressed conditions and maintained it under salt-stress, while sustaining higher but inefficient assimilation rates, leading to starch accumulation and decreased plant biomass, leaf and root area and root length. Narrow conduits in unstressed TT plants were related to permanent restrain of hydraulic conductivity and plant transpiration. Under salinity, TT plants followed the atmospheric water demand, sustained similar transpiration rate from unstressed to salt-stressed conditions and possibly maintained hydraulic integrity, due to likely impaired hydraulic regulation, wider conduits and higher hydraulic conductivity. The accumulation of salts and starch in the TT plants was a strong evidence of salinity tolerance via osmotic regulation, also thought to help to maintain the assimilation rates and transpiration flux under salinity, although it was not translated into higher growth. 相似文献
65.
Background and Aims
The coastal plain of Israel hosts the last few remaining populations of the endemic Iris atropurpurea (Iridaceae), a Red List species of high conservation priority. The flowers offer no nectar reward. Here the role of night-sheltering male solitary bees, honey-bees and female solitary bees as pollinators of I. atropurpurea is documented.Methods
Breeding system, floral longevity, stigma receptivity, visitation rates, pollen loads, pollen deposition and removal and fruit- and seed-set were investigated.Key Results
The main wild pollinators of this plant are male eucerine bees, and to a lesser extent, but with the potential to transfer pollen, female solitary bees. Honey-bees were found to be frequent diurnal visitors; they removed large quantities of pollen and were as effective as male sheltering bees at pollinating this species. The low density of pollen carried by male solitary bees was attributed to grooming activities, pollen displacement when bees aggregated together in flowers and pollen depletion by honey-bees. In the population free of honey-bee hives, male bees carried significantly more pollen grains on their bodies. Results from pollen analysis and pollen deposited on stigmas suggest that inadequate pollination may be an important factor limiting fruit-set. In the presence of honey-bees, eucerine bees were low removal–low deposition pollinators, whereas honey-bees were high removal–low deposition pollinators, because they removed large amounts into corbiculae and deposited relatively little onto receptive stigmas.Conclusions
Even though overall, both bee taxa were equally effective pollinators, we suggest that honey-bees have the potential to reduce the amount of pollen available for plant reproduction, and to reduce the amount of resources available to solitary bee communities. The results of this study have potential implications for the conservation of this highly endangered plant species if hives are permitted inside reserves, where the bulk of Oncocyclus iris species are protected. 相似文献66.
Elaine T. Lim Soumya Raychaudhuri Stephan J. Sanders Christine Stevens Aniko Sabo Daniel G. MacArthur Benjamin M. Neale Andrew Kirby Douglas M. Ruderfer Menachem Fromer Monkol Lek Li Liu Jason Flannick Stephan Ripke Uma Nagaswamy Donna Muzny Jeffrey G. Reid Alicia Hawes Mark J. Daly 《Neuron》2013,77(2):235-242
67.
Nathalia Torres Dutra Vanildo Silveira Inga Gonçalves de Azevedo Lupis Ribeiro Gomes‐Neto Arnoldo Rocha Façanha Neusa Steiner Miguel Pedro Guerra Eny Iochevet Segal Floh Claudete Santa‐Catarina 《Physiologia plantarum》2013,148(1):121-132
Polyamines (PAs) are abundant polycationic compounds involved in many physiological processes in plants, including somatic embryogenesis. This study investigates the role of PAs on cellular growth and structure of pro‐embryogenic masses (PEMs), endogenous PA and proton pump activities in embryogenic suspension cultures of Araucaria angustifolia. The embryogenic suspension cultures were incubated with putrescine (Put), spermidine (Spd), spermine (Spm) and the inhibitor methylglyoxal‐bis(guanylhydrazone) (MGBG), respectively (1 mM). After 24 h and 21 days, the cellular growth and structure of PEMs, endogenous PA contents and proton pump activities were analyzed. The addition of Spm reduced the cellular growth and promoted the development of PEMs in embryogenic cultures, which could be associated with a reduction in the activities of proton pumps, such as H+‐ATPase P‐ and V‐types and H+‐PPases, and alterations in the endogenous PA contents. Spm significantly affected the physiology of the A. angustifolia somatic embryogenesis suspension, as it potentially affects cellular growth and structure of PEMs through the modulation of proton pump activities. This work demonstrates the involvement of exogenous PAs in the modulation of cellular growth and structure of PEMs, endogenous PA levels and proton pump activities during somatic embryogenesis. To our knowledge, this study is the first to report a relationship between PAs and proton pump activities in these processes. The results obtained in this study offer new perspectives for studies addressing the role of PAs and proton pump on somatic embryogenesis in this species. 相似文献
68.
Leeat Keren Ora Zackay Maya Lotan‐Pompan Uri Barenholz Erez Dekel Vered Sasson Guy Aidelberg Anat Bren Danny Zeevi Adina Weinberger Uri Alon Ron Milo Eran Segal 《Molecular systems biology》2013,9(1)
Most genes change expression levels across conditions, but it is unclear which of these changes represents specific regulation and what determines their quantitative degree. Here, we accurately measured activities of ~900 S. cerevisiae and ~1800 E. coli promoters using fluorescent reporters. We show that in both organisms 60–90% of promoters change their expression between conditions by a constant global scaling factor that depends only on the conditions and not on the promoter's identity. Quantifying such global effects allows precise characterization of specific regulation—promoters deviating from the global scale line. These are organized into few functionally related groups that also adhere to scale lines and preserve their relative activities across conditions. Thus, only several scaling factors suffice to accurately describe genome‐wide expression profiles across conditions. We present a parameter‐free passive resource allocation model that quantitatively accounts for the global scaling factors. It suggests that many changes in expression across conditions result from global effects and not specific regulation, and provides means for quantitative interpretation of expression profiles. 相似文献
69.
70.
Gross Menachem Ashqar Fadi Sionov Ronit Vogt Friedman Michael Eliashar Ron Zaks Batya Gati Irith Duanis-Assaf Danielle Feldman Mark Steinberg Doron 《International microbiology》2022,25(1):177-187
International Microbiology - In this study, we aimed to develop a novel, sustained release varnish (SRV) for voice prostheses (VP) releasing chlorhexidine (CHX), for the prevention of biofilm... 相似文献