首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1263篇
  免费   81篇
  2021年   11篇
  2020年   8篇
  2019年   7篇
  2018年   7篇
  2017年   11篇
  2016年   11篇
  2015年   64篇
  2014年   81篇
  2013年   76篇
  2012年   104篇
  2011年   104篇
  2010年   76篇
  2009年   59篇
  2008年   45篇
  2007年   27篇
  2006年   32篇
  2005年   15篇
  2004年   33篇
  2003年   30篇
  2002年   27篇
  2001年   19篇
  2000年   23篇
  1999年   22篇
  1998年   14篇
  1997年   11篇
  1996年   15篇
  1995年   8篇
  1994年   19篇
  1993年   14篇
  1992年   28篇
  1991年   11篇
  1990年   19篇
  1989年   23篇
  1988年   19篇
  1987年   15篇
  1986年   13篇
  1985年   9篇
  1984年   9篇
  1983年   9篇
  1982年   10篇
  1981年   9篇
  1980年   12篇
  1979年   14篇
  1978年   10篇
  1977年   7篇
  1976年   8篇
  1975年   11篇
  1973年   9篇
  1971年   10篇
  1969年   7篇
排序方式: 共有1344条查询结果,搜索用时 62 毫秒
61.
Abstract

Post-construction avifauna investigations were undertaken at Project West Wind, Meridian Energy Limited's 62-turbine wind farm on the Wellington south coast. These investigations were required in accordance with the resource consent conditions to quantify the level of avian mortalities occurring at the wind farm, particularly in regard to New Zealand falcon (Falco novaeseelandiae), kākā (Nestor meridionalis) and kererū (Hemiphaga novaeseelandiae). This is the first comprehensive study at a New Zealand operating wind farm. The methods included three field components necessary to calculate annual estimates of mortalities across the wind farm site: routine turbine searches; carcass detection trials; and carcass removal trials. Results from years 1 and 2 of a three-year programme are presented. To date, mortalities have been recorded for 17 taxa at 18 of the 24 study turbines. There have been no recorded mortalities of falcon, kākā or kererū. Australasian harrier (Circus approximans) has been the species for which the most mortalities have been recorded. Overall estimated annual mortality rates for years 1 and 2 were calculated to be approximately six and five birds per turbine respectively.  相似文献   
62.
This is an account of the movement of photography as art into the objectivity of the camera image as scientific evidence. On arrival at Cornell University, Collier did not appreciate the extreme flexibility of this department, primarily dedicated to applied anthroplogy, and thereby more open to diverse human data than other branches of the field. The action‐problem‐solving Cornell students and behavioral specialists leapt over theoretical obstacles and directly utilized photographic insights both projectively and in precise content analysis. But the future challenge of visual anthropology came with the text of the moving image and the completeness of filmic understanding.  相似文献   
63.
A LS Houde  C C Wilson  B D Neff 《Heredity》2013,111(6):513-519
The additive genetic effects of traits can be used to predict evolutionary trajectories, such as responses to selection. Non-additive genetic and maternal environmental effects can also change evolutionary trajectories and influence phenotypes, but these effects have received less attention by researchers. We partitioned the phenotypic variance of survival and fitness-related traits into additive genetic, non-additive genetic and maternal environmental effects using a full-factorial breeding design within two allopatric populations of Atlantic salmon (Salmo salar). Maternal environmental effects were large at early life stages, but decreased during development, with non-additive genetic effects being most significant at later juvenile stages (alevin and fry). Non-additive genetic effects were also, on average, larger than additive genetic effects. The populations, generally, did not differ in the trait values or inferred genetic architecture of the traits. Any differences between the populations for trait values could be explained by maternal environmental effects. We discuss whether the similarities in architectures of these populations is the result of natural selection across a common juvenile environment.  相似文献   
64.
We have visualized by cryo‐electron microscopy (cryo‐EM) the complex of the anthrax protective antigen (PA) translocon and the N‐terminal domain of anthrax lethal factor (LFN) inserted into a nanodisc model lipid bilayer. We have determined the structure of this complex at a nominal resolution of 16 Å by single‐particle analysis and three‐dimensional reconstruction. Consistent with our previous analysis of negatively stained unliganded PA, the translocon comprises a globular structure (cap) separated from the nanodisc bilayer by a narrow stalk that terminates in a transmembrane channel (incompletely distinguished in this reconstruction). The globular cap is larger than the unliganded PA pore, probably due to distortions introduced in the previous negatively stained structures. The cap exhibits larger, more distinct radial protrusions, previously identified with PA domain three, fitted by elements of the NMFF PA prepore crystal structure. The presence of LFN, though not distinguished due to the seven‐fold averaging used in the reconstruction, contributes to the distinct protrusions on the cap rim volume distal to the membrane. Furthermore, the lumen of the cap region is less resolved than the unliganded negatively stained PA, due to the low contrast obtained in our images of this specimen. Presence of the LFN extended helix and N terminal unstructured regions may also contribute to this additional internal density within the interior of the cap. Initial NMFF fitting of the cryoEM‐defined PA pore cap region positions the Phe clamp region of the PA pore translocon directly above an internal vestibule, consistent with its role in toxin translocation.  相似文献   
65.
The primary aim of this review was to evaluate the state of knowledge of the geographical distribution of all infectious diseases of clinical significance to humans. A systematic review was conducted to enumerate cartographic progress, with respect to the data available for mapping and the methods currently applied. The results helped define the minimum information requirements for mapping infectious disease occurrence, and a quantitative framework for assessing the mapping opportunities for all infectious diseases. This revealed that of 355 infectious diseases identified, 174 (49%) have a strong rationale for mapping and of these only 7 (4%) had been comprehensively mapped. A variety of ambitions, such as the quantification of the global burden of infectious disease, international biosurveillance, assessing the likelihood of infectious disease outbreaks and exploring the propensity for infectious disease evolution and emergence, are limited by these omissions. An overview of the factors hindering progress in disease cartography is provided. It is argued that rapid improvement in the landscape of infectious diseases mapping can be made by embracing non-conventional data sources, automation of geo-positioning and mapping procedures enabled by machine learning and information technology, respectively, in addition to harnessing labour of the volunteer ‘cognitive surplus’ through crowdsourcing.  相似文献   
66.
The anthrax toxin receptors, ANTXR1 and ANTXR2, act as molecular clamps to prevent the protective antigen (PA) toxin subunit from forming pores until exposure to low pH. PA forms pores at pH approximately 6.0 or below when it is bound to ANTXR1, but only at pH approximately 5.0 or below when it is bound to ANTXR2. Here, structure-based mutagenesis was used to identify non-conserved ANTXR2 residues responsible for this striking 1.0 pH unit difference in pH threshold. Residues conserved between ANTXR2 and ANTXR1 that influence the ANTXR2-associated pH threshold of pore formation were also identified. All of these residues contact either PA domain 2 or the neighboring edge of PA domain 4. These results provide genetic evidence for receptor release of these regions of PA as being necessary for the protein rearrangements that accompany anthrax toxin pore formation.  相似文献   
67.
68.
Insulin-like growth factors (IGFs) I and II (IGF-I, IGF-II) and Des-3-IGF-I at physiological concentrations are potent mitogens of bovine undifferentiated mammary epithelial cells cultured in collagen in a serum-free medium. Des-3-IGF-I was found to be as potent as IGF-I, while IGF-II was significantly less active. All three factors acted either synergistically or additively with epidermal growth factor (EGF), cholera toxin and fetal calf serum (FCS). Indirect evidence indicates that despite its lower mitogenic activity the action of IGF-II is mediated through IGF-I receptors. The galactopoietic activity of Des-3-IGF-I and IGF-II was studied in an organ culture of bovine lactating mammary glands using lactogen-responsive fat synthesis as a test. Neither Des-3-IGF-I nor IGF-II exhibited galactopoietic activity nor did they affect the galactopoietic activity of prolactin.  相似文献   
69.
Bcl-2 and Bcl-XL prevent neuronal apoptosis during development, neurodegenerative disease, and trauma. To test a new anti-apoptosis strategy for neuroprotection, we engineered nontoxic components of anthrax toxin into a Bcl-XL delivery system. Delivery of Bcl-XL by this system prevented apoptosis of cultured rat cerebellar granule cells and macrophages, and the prevention depended on both the Bcl-XL and the anthrax toxin receptor binding/translocation moieties. Furthermore, neuronal death in vivo in a retinal ganglion cell model of axotomy-induced apoptosis was inhibited by administration of this fusion protein. Thus, Bcl-XL protein can be delivered into cells from the medium or interstitial space, offering a new way to block apoptosis upstream of many caspases and the mitochondria dysfunction phase of apoptosis.  相似文献   
70.
African killifishes (Cyprinodontiformes, Aplocheilidae) historically associated with the genus Aphyosemion occur in two geographically distinct regions. One assemblage from far West Africa has been previously shown to be monophyletic and not closely related to the remaining eastern species of Aphyosemion (W. J. Murphy and G. E. Collier, 1997, Mol. Biol. Evol. 14, 790-799). This is supported by further analysis of mitochondrial DNA sequences from 19 species from 21 different localities, representing 19 of the putative 22 species of this western group. Phylogenetic analyses of these data corroborate the monophyly and sister-group relationship of two distinct groups of taxa: Callopanchax and Scriptaphyosemion. Many of the relationships within Scriptaphyosemion suggest that these taxa may have radiated within a short period of time relative to the rate of substitutions within these sequences. A third, and possibly paraphyletic group of species, Archiaphyosemion, is suggested to be the sister taxon to the first two groups. These three groups are elevated to generic rank and together represent the sister group to the genus Epiplatys. Biogeographic inference suggests that the ancestors of this group diversified westward through upland habitat and have only relatively recently entered the lowland habitats in which Scriptaphyosemion and Callopanchax have diversified, with the latter genus reacquiring a suite of traits collectively referred to as annualism.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号