全文获取类型
收费全文 | 1831篇 |
免费 | 140篇 |
国内免费 | 1篇 |
出版年
2023年 | 4篇 |
2022年 | 25篇 |
2021年 | 37篇 |
2020年 | 13篇 |
2019年 | 25篇 |
2018年 | 35篇 |
2017年 | 26篇 |
2016年 | 58篇 |
2015年 | 104篇 |
2014年 | 115篇 |
2013年 | 112篇 |
2012年 | 180篇 |
2011年 | 136篇 |
2010年 | 96篇 |
2009年 | 91篇 |
2008年 | 123篇 |
2007年 | 115篇 |
2006年 | 93篇 |
2005年 | 87篇 |
2004年 | 103篇 |
2003年 | 89篇 |
2002年 | 84篇 |
2001年 | 18篇 |
2000年 | 16篇 |
1999年 | 23篇 |
1998年 | 29篇 |
1997年 | 14篇 |
1996年 | 18篇 |
1995年 | 8篇 |
1994年 | 11篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 2篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1973年 | 2篇 |
1925年 | 1篇 |
排序方式: 共有1972条查询结果,搜索用时 15 毫秒
71.
72.
Stable preanaphase spindle positioning requires Bud6p and an apparent interaction between the spindle pole bodies and the neck 下载免费PDF全文
Faithful partitioning of genetic material during cell division requires accurate spatial and temporal positioning of nuclei within dividing cells. In Saccharomyces cerevisiae, nuclear positioning is regulated by an elegant interplay between components of the actin and microtubule cytoskeletons. Regulators of this process include Bud6p (also referred to as the actin-interacting protein Aip3p) and Kar9p, which function to promote contacts between cytoplasmic microtubule ends and actin-delimited cortical attachment points. Here, we present the previously undetected association of Bud6p with the cytoplasmic face of yeast spindle pole bodies, the functional equivalent of metazoan centrosomes. Cells lacking Bud6p show exaggerated movements of the nucleus between mother and daughter cells and display reduced amounts of time a given spindle pole body spends in close association with the neck region of budding cells. Furthermore, overexpression of BUD6 greatly enhances interactions between the spindle pole body and mother-bud neck in a spindle alignment-defective dynactin mutant. These results suggest that association of either spindle pole body with neck components, rather than simply entry of a spindle pole body into the daughter cell, provides a positive signal for the progression of mitosis. We propose that Bud6p, through its localization at both spindle pole bodies and at the mother-bud neck, supports this positive signal and provides a regulatory mechanism to prevent excessive oscillations of preanaphase nuclei, thus reducing the likelihood of mitotic delays and nuclear missegregation. 相似文献
73.
Astrid Schnetzer Peter E. Miller Rebecca A. Schaffner Beth A. Stauffer Burton H. Jones Stephen B. Weisberg Paul M. DiGiacomo William M. Berelson David A. Caron 《Harmful algae》2007,6(3):372-387
Abundances of Pseudo-nitzschia spp. and concentrations of particulate domoic acid (DA) were determined in the Southern California Bight (SCB) along the coasts of Los Angeles and Orange Counties during spring and summer of 2003 and 2004. At least 1500 km2 were affected by a toxic event in May/June of 2003 when some of the highest particulate DA concentrations reported for US coastal waters were measured inside the Los Angeles harbor (12.7 μg DA L−1). Particulate DA levels were an order of magnitude lower in spring of 2004 (February and March), but DA concentrations per cell at several sampling stations during 2004 exceeded previously reported maxima for natural populations of Pseudo-nitzschia (mean = 24 pg DA cell−1, range = 0–117 pg DA cell−1). Pseudo-nitzschia australis dominated the Pseudo-nitzschia assemblage in spring 2004. Overall, DA-poisoning was implicated in >1400 mammal stranding incidents within the SCB during 2003 and 2004. Ancillary physical and chemical data obtained during our regional surveys in 2004 revealed that Pseudo-nitzschia abundances, particulate DA and cellular DA concentrations were inversely correlated with concentrations of silicic acid, nitrogen and phosphate, and to specific nutrient ratios. Particulate DA was detected in sediment traps deployed at 550 and 800 m depth during spring of 2004 (0.29–7.6 μg DA (g sediment dry weight)−1). The highest DA concentration in the traps was measured within 1 week of dramatic decreases in the abundances of Pseudo-nitzschia in surface waters. To our knowledge these are the deepest sediment trap collections from which DA has been detected. Sinking of the spring Pseudo-nitzschia bloom may constitute a potentially important link between DA production in surface waters and benthic communities in the coastal ocean near Los Angeles. Our study indicates that toxic blooms of Pseudo-nitzschia are a recurring phenomenon along one of the most densely populated coastal stretches of the SCB and that the severity and magnitude of these events can be comparable to or greater than these events in other geographical regions affected by domoic acid. 相似文献
74.
Cappuyns AM Bernaerts K Smets IY Ona O Prinsen E Vanderleyden J Van Impe JF 《Biotechnology progress》2007,23(5):1074-1081
In this paper the problem of reliable and accurate parameter estimation for unstructured models is considered. It is illustrated how a theoretically optimal design can be successfully translated into a practically feasible, robust, and informative experiment. The well-known parameter estimation problem of Monod kinetic parameters is used as a vehicle to illustrate our approach. As known for a long time, noisy batch measurements do not allow for unique and accurate estimation of the kinetic parameters of the Monod model. Techniques of optimal experiment design are, therefore, exploited to design informative experiments and to improve the parameter estimation accuracy. During the design process, practical feasibility has to be kept in mind. The designed experiments are easy to implement in practice and do not require additional monitoring equipment. Both design and experimental validation of informative fed batch experiments are illustrated with a case study, namely, the growth of the nitrogen-fixing bacteria Azospirillum brasilense. 相似文献
75.
Sren Toft Elsa Cuende Astrid Louise Olesen Anne Mathiesen Maria Meisner Larsen Kim Jensen 《Oikos》2019,128(10):1467-1477
Habitats vary in food resources with carnivores often being prey limited, but it is unclear whether habitats facilitate a nutritionally balanced diet. Two paradigms in nutritional ecology, ecological stoichiometry and nutritional geometry, predict that carnivores are limited mainly by protein or lipid, respectively. Using the carabid beetle Anchomenus dorsalis and 10 other predatory beetles from agricultural fields, we developed and tested two simple procedures for quantifying macronutrient‐specific habitat conditions without requiring information about the natural prey. Both procedures assume that predators forage for nutrients rather than specific prey. Our results show that 10 of 11 species were food limited. Five species were lipid limited and one species was protein limited in the field. Co‐existing predator species showed considerable segregation of fundamental macronutritional niches. A linear relationship between specific nutrient limitation and the target lipid:protein (L:P) intake ratio indicates that species with high L:P target are more protein limited while species with low L:P target are more lipid limited. The study illustrates how species within a natural assemblage vary in nutritional niche and in specific nutrient limitation. 相似文献
76.
Inês Chaves Bram van der Eerden Ruben Boers Joachim Boers Astrid A. Streng Yanto Ridwan 《Chronobiology international》2019,36(5):657-671
Circadian rhythm disturbance (CRD) increases the risk of disease, e.g. metabolic syndrome, cardiovascular disease, and cancer. In the present study, we investigated later life adverse health effects triggered by repeated jet lag during gestation. Pregnant mice were subjected to a regular light-dark cycle (CTRL) or to a repeated delay (DEL) or advance (ADV) jet lag protocol. Both DEL and ADV offspring showed reduced weight gain. ADV offspring had an increased circadian period, and an altered response to a jet lag was observed in both DEL and ADV offspring. Analysis of the bones of adult male ADV offspring revealed reduced cortical bone mass and strength. Strikingly, analysis of the heart identified structural abnormalities and impaired heart function. Finally, DNA methylation analysis revealed hypermethylation of miR17-92 cluster and differential methylation within circadian clock genes, which correlated with altered gene expression. We show that developmental CRD affects the circadian system and predisposes to non-communicable disease in adult life. 相似文献
77.
78.
Gregor Schlüter Arzu Celik Renato Obata Mike Schlicker Sigrun Hofferbert Astrid Schlung Ibrahim M. Adham Wolfgang Engel 《Molecular reproduction and development》1996,43(1):1-6
Structural data are presented on the protamine gene cluster (PGC) of human, mouse, rat, and bull. By restriction mapping we demonstrate that the organization of the protamine cluster is conserved throughout all four species, i.e., the genes are situated in a head to tail arrangement in the order: protamine l-protamine 2-transition protein 2. Further, we established the nucleotide sequence of the entire human PGC (25 kb in total) and the 3′ portion of the rat protamine cluster (PRM2 and TNP2 genes and intergenic region). In addition, a 1 kb fragment of the bovine and murine protamine cluster, situated between PRM2 and TNP2, was sequenced. This fragment is conserved regarding sequence, position, and orientation in all species examined, and was classified as likely coding region by gene recognition program GRAIL. Using the rat fragment as a probe in RNA blots, we detected a testis-specific signal of about 0.5 kb. Finally, we demonstrate a high density of Alu elements, both full and fragmented copies, in the human PGC and discuss their localization with respect to evolutionary and functional aspects. © 1996 Wiley-Liss, Inc. 相似文献
79.
80.
Growth of Nitrosomonas europaea on hydroxylamine 总被引:2,自引:0,他引:2
Peter de Bruijn Astrid A. Van de Graaf Mike S.M. Jetten Lesley A. Robertson J. Gijs Kuenen 《FEMS microbiology letters》1995,125(2-3):179-184
Abstract Hydroxylamine is an intermediate in the oxidation of ammonia to nitrite, but until now it has not been possible to grow Nitrosomonas europaea on hydroxylamine. This study demonstrates that cells of N. europaea are capable of growing mixotrophically on ammonia and hydroxylamine. The molar growth yield on hydroxylamine (4.74 g mol−1 at a growth rate of 0.03 h−1 ) was higher than expected. Aerobically growing cells of N. europaea oxidized ammonia to nitrite with little loss of inorganic nitrogen, while significant inorganic nitrogen losses occurred when cells were growing mixotrophically on ammonia and hydroxylamine. In the absence of oxygen, hydroxylamine was oxidized with nitrite as electron acceptor, while nitrous oxide was produced. Anaerobic growth of N. europaea on ammonium, hydroxylamine and nitrite could not be observed at growth rates of 0.03 h−1 and 0.01 h−1 . 相似文献