全文获取类型
收费全文 | 8338篇 |
免费 | 942篇 |
国内免费 | 1篇 |
专业分类
9281篇 |
出版年
2021年 | 100篇 |
2019年 | 65篇 |
2018年 | 110篇 |
2017年 | 102篇 |
2016年 | 139篇 |
2015年 | 266篇 |
2014年 | 283篇 |
2013年 | 377篇 |
2012年 | 420篇 |
2011年 | 420篇 |
2010年 | 278篇 |
2009年 | 223篇 |
2008年 | 368篇 |
2007年 | 405篇 |
2006年 | 348篇 |
2005年 | 365篇 |
2004年 | 325篇 |
2003年 | 303篇 |
2002年 | 293篇 |
2001年 | 166篇 |
2000年 | 174篇 |
1999年 | 143篇 |
1998年 | 125篇 |
1997年 | 122篇 |
1996年 | 104篇 |
1995年 | 97篇 |
1994年 | 115篇 |
1993年 | 100篇 |
1992年 | 160篇 |
1991年 | 128篇 |
1990年 | 113篇 |
1989年 | 119篇 |
1988年 | 109篇 |
1987年 | 125篇 |
1986年 | 97篇 |
1985年 | 137篇 |
1984年 | 144篇 |
1983年 | 106篇 |
1982年 | 125篇 |
1981年 | 115篇 |
1980年 | 102篇 |
1979年 | 93篇 |
1978年 | 65篇 |
1977年 | 70篇 |
1976年 | 79篇 |
1975年 | 63篇 |
1974年 | 76篇 |
1973年 | 65篇 |
1972年 | 57篇 |
1971年 | 55篇 |
排序方式: 共有9281条查询结果,搜索用时 0 毫秒
901.
Was monogamy a key step on the hominin road? reevaluating the monogamy hypothesis in the evolution of cooperative breeding 下载免费PDF全文
Because human mothers routinely rely on others to help raise their young, humans have been characterized as cooperative breeders.1–9 Several large‐scale phylogenetic analyses have presented compelling evidence that monogamy preceded the evolution of cooperative breeding in a wide variety of nonhuman animals.10–14 These studies have suggested that monogamy provides a general rule (the monogamy hypothesis) for explaining evolutionary transitions to cooperative breeding.15 Given the prevalence of cooperative breeding in contemporary human societies, we evaluate whether this suggests a monogamous hominin past. 相似文献
902.
David J. Aceti Craig A. Bingman Russell L. Wrobel Ronnie O. Frederick Shin-ichi Makino Karl W. Nichols Sarata C. Sahu Lai F. Bergeman Paul G. Blommel Claudia C. Cornilescu Katarzyna A. Gromek Kory D. Seder Soyoon Hwang John G. Primm Grzegorz Sabat Frank C. Vojtik Brian F. Volkman Zsolt Zolnai George N. Phillips Jr. John L. Markley Brian G. Fox 《Journal of structural and functional genomics》2015,16(2):67-80
903.
Sandra Lavorel Matthew J. Colloff Sue Mcintyre Michael D. Doherty Helen T. Murphy Daniel J. Metcalfe Michael Dunlop Richard J. Williams Russell M. Wise Kristen J. Williams 《Global Change Biology》2015,21(1):12-31
Ecosystem services are typically valued for their immediate material or cultural benefits to human wellbeing, supported by regulating and supporting services. Under climate change, with more frequent stresses and novel shocks, 'climate adaptation services', are defined as the benefits to people from increased social ability to respond to change, provided by the capability of ecosystems to moderate and adapt to climate change and variability. They broaden the ecosystem services framework to assist decision makers in planning for an uncertain future with new choices and options. We present a generic framework for operationalising the adaptation services concept. Four steps guide the identification of intrinsic ecological mechanisms that facilitate the maintenance and emergence of ecosystem services during periods of change, and so materialise as adaptation services. We applied this framework for four contrasted Australian ecosystems. Comparative analyses enabled by the operational framework suggest that adaptation services that emerge during trajectories of ecological change are supported by common mechanisms: vegetation structural diversity, the role of keystone species or functional groups, response diversity and landscape connectivity, which underpin the persistence of function and the reassembly of ecological communities under severe climate change and variability. Such understanding should guide ecosystem management towards adaptation planning. 相似文献
904.
905.
906.
David B. Lindenmayer Emma L. Burns Philip Tennant Chris R. Dickman Peter T. Green David A. Keith Daniel J. Metcalfe Jeremy Russell‐Smith Glenda M. Wardle Dick Williams Karl Bossard Claire deLacey Ivan Hanigan C. Michael Bull Graeme Gillespie Richard J. Hobbs Charles J. Krebs Gene E. Likens John Porter Michael Vardon 《Austral ecology》2015,40(3):213-224
In 2050, which aspects of ecosystem change will we regret not having measured? Long‐term monitoring plays a crucial part in managing Australia's natural environment because time is a key factor underpinning changes in ecosystems. It is critical to start measuring key attributes of ecosystems – and the human and natural process affecting them – now, so that we can track the trajectory of change over time. This will facilitate informed choices about how to manage ecological changes (including interventions where they are required) and promote better understanding by 2050 of how particular ecosystems have been shaped over time. There will be considerable value in building on existing long‐term monitoring programmes because this can add significantly to the temporal depth of information. The economic and social processes driving change in ecosystems are not identical in all ecosystems, so much of what is monitored (and the means by which it is monitored) will most likely target specific ecosystems or groups of ecosystems. To best understand the effects of ecosystem‐specific threats and drivers, monitoring also will need to address the economic and social factors underpinning ecosystem‐specific change. Therefore, robust assessments of the state of Australia's environment will be best achieved by reporting on the ecological performance of a representative sample of ecosystems over time. Political, policy and financial support to implement appropriate ecosystem‐specific monitoring is a perennial problem. We suggest that the value of ecological monitoring will be demonstrable, when plot‐based monitoring data make a unique and crucial contribution to Australia's ability to produce environmental accounts, environmental reports (e.g. the State of the Environment, State of the Forests) and to fulfilling reporting obligations under international agreements, such as the Convention on Biological Diversity. This paper suggests what must be done to meet Australia's ecological information needs by 2050. 相似文献
907.
The mammalian target of rapamycin (mTOR) is a kinase that responds to a myriad of signals, ranging from nutrient availability and energy status, to cellular stressors, oxygen sensors and growth factors. The finely tuned response of mTOR to these stimuli results in alterations to cell metabolism and cell growth. Recent studies of conditional knockouts of mTOR pathway components in mice have affirmed the role of mTOR signaling in energy balance, both at the cell and whole organism levels. Such studies have also highlighted a role for mTOR in stem cell homeostasis and lifespan determination. Here, we discuss the molecular mechanisms of TOR signaling and review recent in vitro and in vivo studies of mTOR tissue-specific activities in mammals. 相似文献
908.
909.
A new form of high surface area bioelectrode, based on nanofibers of electrospun gold with immobilized fructose dehydrogenase, was developed. The gold fibers were prepared by electroless deposition of gold nanoparticles on an electrospun poly(acrylonitrile)-HAuCl(4) fiber. The material was characterized using electron microscopy, XRD and BET, as well as cyclic voltammetry and biochemical assay of the immobilized enzyme. The electrochemical surface area of the gold microfibers was 0.32 ± 0.04 m(2)/g. Fructose dehydrogenase was covalently coupled to the gold surface through glutaraldehyde crosslinks to a cystamine monolayer. The enzyme exhibited mediated electron transfer directly to the gold electrode and catalytic currents characteristic of fructose oxidation in the presence of a ferrocene methanol mediator were observed. The limit of detection of fructose was 11.7 μM and the K(M) of the immobilized enzyme was 5mM. The microfiber electrode was stable over 20 cycles with a 3.05% standard deviation. The response time of the sensor was less than 2.2s and reached half maximum value within 3.6s. The sensor was proven to be accurate and precise in both serum and popular beverages sweetened with high fructose corn syrup. The addition of glucose isomerase enabled the sensor to perform with glucose, thus expanding the available analyte selection for the sensor. 相似文献
910.
Caplan J Niethammer M Taylor RM Czymmek KJ 《Current opinion in structural biology》2011,21(5):686-693
Correlative microscopy is a sophisticated approach that combines the capabilities of typically separate, but powerful microscopy platforms: often including, but not limited, to conventional light, confocal and super-resolution microscopy, atomic force microscopy, transmission and scanning electron microscopy, magnetic resonance imaging and micro/nano CT (computed tomography). When targeting rare or specific events within large populations or tissues, correlative microscopy is increasingly being recognized as the method of choice. Furthermore, this multi-modal assimilation of technologies provides complementary and often unique information, such as internal and external spatial, structural, biochemical and biophysical details from the same targeted sample. The development of a continuous stream of cutting-edge applications, probes, preparation methodologies, hardware and software developments will enable realization of the full potential of correlative microscopy. 相似文献