全文获取类型
收费全文 | 2757篇 |
免费 | 227篇 |
国内免费 | 3篇 |
出版年
2023年 | 10篇 |
2022年 | 18篇 |
2021年 | 55篇 |
2020年 | 30篇 |
2019年 | 35篇 |
2018年 | 38篇 |
2017年 | 35篇 |
2016年 | 73篇 |
2015年 | 107篇 |
2014年 | 120篇 |
2013年 | 159篇 |
2012年 | 256篇 |
2011年 | 206篇 |
2010年 | 141篇 |
2009年 | 132篇 |
2008年 | 191篇 |
2007年 | 175篇 |
2006年 | 194篇 |
2005年 | 153篇 |
2004年 | 195篇 |
2003年 | 146篇 |
2002年 | 137篇 |
2001年 | 32篇 |
2000年 | 14篇 |
1999年 | 33篇 |
1998年 | 34篇 |
1997年 | 28篇 |
1996年 | 17篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 29篇 |
1992年 | 18篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 17篇 |
1988年 | 11篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 13篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 4篇 |
1974年 | 2篇 |
1969年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有2987条查询结果,搜索用时 0 毫秒
211.
Finding NEMO: nestedness engendered by mutualistic organization in anemonefish and their hosts 总被引:2,自引:0,他引:2
Ollerton J McCollin D Fautin DG Allen GR 《Proceedings. Biological sciences / The Royal Society》2007,274(1609):591-598
The interaction structure of mutualistic relationships, in terms of relative specialization of the partners, is important to understanding their ecology and evolution. Analyses of the mutualistic interaction between anemonefish and their host sea anemones show that the relationship is highly nested in structure, generalist species interacting with one another and specialist species interacting mainly with generalists. This supports the hypothesis that the configuration of mutualistic interactions will tend towards nestedness. In this case, the structure of the interaction is at a much larger scale than previously hypothesized, across more than 180 degrees of longitude and some 60 degrees of latitude, probably owing to the pelagic dispersal capabilities of these species in a marine environment. Additionally, we found weak support for the hypothesis that geographically widespread species should be more generalized in their interactions than species with small ranges. This study extends understanding of the structure of mutualistic relationships into previously unexplored taxonomic and physical realms, and suggests how nestedness analysis can be applied to the conservation of obligate species interactions. 相似文献
212.
Elzein E Kalla R Li X Perry T Marquart T Micklatcher M Li Y Wu Y Zeng D Zablocki J 《Bioorganic & medicinal chemistry letters》2007,17(1):161-166
A series of new selective, high affinity A(1)-AdoR agonists is reported. Compound 23 that incorporated a carboxylic acid functionality in the 4-position of the pyrazole ring displayed K(iL) value of 1 nM for the A(1)-AdoR and >5000-fold selectivity over the A(3) and A(2A)-AdoRs. In addition, compound 19 that incorporated a carboxamide functionality in the 4-position of the pyrazole ring displayed subnanomolar affinity for the A(1)-AdoR (K(iL)=0.6 nM) and >600-fold selectivity over the A(3) and A(2A)-AdoRs. 相似文献
213.
Gilad AA McMahon MT Walczak P Winnard PT Raman V van Laarhoven HW Skoglund CM Bulte JW van Zijl PC 《Nature biotechnology》2007,25(2):217-219
Existing magnetic resonance reporter genes all rely on the presence of (super)paramagnetic substances and employ water relaxation to gain contrast. We designed a nonmetallic, biodegradable, lysine rich-protein (LRP) reporter, the prototype of a potential family of genetically engineered reporters expressing artificial proteins with frequency-selective contrast. This endogenous contrast, based on transfer of radiofrequency labeling from the reporter's amide protons to water protons, can be switched on and off. 相似文献
214.
Listeria as a vaccine vector 总被引:3,自引:0,他引:3
The immunostimulatory characteristics and intracellular niche of Listeria monocytogenes make it uniquely suitable for use as a live bacterial vaccine vector. Preclinical results supporting this idea, and current strategies to induce beneficial cell-mediated immunity to both infectious diseases and cancer with this vector, are discussed in this review. 相似文献
215.
POFs: what we don't know can hurt us 总被引:1,自引:0,他引:1
Over a quarter of all eukaryotic genes encode proteins with obscure features that lack currently defined motifs or domains (POFs). Interestingly, most of the differences in gene repertoire among species were recently found to be attributed to POFs. A comparison of the Arabidopsis, rice and poplar genomes reveals that Arabidopsis contains 5069 POFs, of which 2045 have no obvious homologs in rice or poplar and are likely to be involved in species- or phylogenetic-specific functions in Arabidopsis. The study of POFs is an important endeavor that will shed much needed light on the genetic properties that make any given plant species unique. Furthermore, with respect to many species-specific features, such studies show that we seem to be limited in what we can expect to learn from a model plant such as Arabidopsis. 相似文献
216.
Lisa J. Natanson James A. Sulikowski Jeff R. Kneebone Paul C. Tsang 《Environmental Biology of Fishes》2007,80(2-3):293-308
Age and growth estimates for the smooth skate, Malacoraja senta, were derived from 306 vertebral centra from skates caught in the North Atlantic off the coast of New Hampshire and Massachusetts, USA. Males and females were aged to 15 and 14 years, respectively. Male and female growth diverged at both ends of the data range and the sexes required different growth functions to describe them. Males followed a traditional growth scenario and were best described by a von Bertalanffy curve with a set L o (11 cm TL) where L inf = 75.4 cm TL, K = 0.12. Females required the use of back-calculated values to account for a lack of small individuals, using these data they were best described by a von Bertalanffy curve where growth parameters derived from vertebral length-at-age data are L inf = 69.6 cm TL, K = 0.12, and L o = 10. 相似文献
217.
James A. Sulikowski William B. Driggers III G. Walter Ingram Jr. Jeff Kneebone Darren E. Ferguson Paul C. W. Tsang 《Environmental Biology of Fishes》2007,80(2-3):285-292
Information regarding sexual maturity and reproductive cycles in skates has largely been based on gross morphological changes
within the reproductive tract. While this information has proved valuable in obtaining life history information, it also necessitates
sacrificing the skates to obtain this data. In contrast, few studies have used circulating steroid hormones to establish when
these batoids become reproductively capable or for the determination of reproductive cyclicity. This study summarizes our
current knowledge of hormonal analyses in determining skate reproductive status and offers information that suggests analysis
of circulating steroid hormone concentrations provide a means to determine size at sexual maturity and asses reproductive
cycles without the need to sacrifice the skate. 相似文献
218.
Jeff Kneebone Darren E. Ferguson James A. Sulikowski Paul C. W. Tsang 《Environmental Biology of Fishes》2007,80(2-3):257-265
The smooth skate, Malacoraja senta, and thorny skate, Amblyraja radiata, are two commercially exploited batoids found within the Gulf of Maine. During the past five years, we conducted a large
study to accurately describe important biological life history parameters previously lacking for these species. As part of
that project, the current study reports our findings on the hormonal profiles associated with the reproductive cycles of M. senta and A. radiata. Blood samples were obtained from mature M. senta and A. radiata of both sexes from all months of the year, and plasma testosterone (T), estradiol (E2) and progesterone (P4) concentrations were determined using radioimmunoassay (RIA). In female M. senta and A. radiata, monthly T concentrations ranged from 4,522 pg ml−1 to 1,373 pg ml−1 and 31,940 pg ml−1 to 14,428 pg ml−1, E2 concentrations from 831 pg ml−1 to 60 pg ml−1 and 8,515 pg ml−1 to 2,902 pg ml−1, and P4 concentrations from 3,027 pg ml−1 to 20 pg ml−1 and 3,264 pg ml−1 to 331 pg ml−1, respectively. No statistical differences were detected between any months for any hormone. Estradiol concentrations were
not correlated with ovary weight, shell gland weight, or diameter of the largest follicles in either species. Monthly T concentrations
in male M. senta and A. radiata ranged from 23,146 to 12,660 pg ml−1 and from 57,500pg ml−1 to 24,737 pg ml−1, while E2 concentrations ranged from 7.5 pg ml−1 to undetectable and 103 to 30 pg ml−1, respectively. No statistical differences were observed between months for either steroid. Testosterone concentrations were
weakly correlated with testes weight and percent of stage VI spermatocysts in A. radiata, however, no correlation was detected between T and stage VI spermatocysts in M. senta. Collectively, these data support the previous conclusion that M. senta and A. radiata of both sexes are capable of reproducing year round in the western Gulf of Maine. 相似文献
219.
Arendt J 《Biological reviews of the Cambridge Philosophical Society》2007,82(2):241-256
Body size is important to most aspects of biology and is also one of the most labile traits. Despite its importance we know remarkably little about the proximate (developmental) factors that determine body size under different circumstances. Here, I review what is known about how cell size and number contribute to phenetic and genetic variation in body size in Drosophila melanogaster, several fish, and fruits and leaves of some angiosperms. Variation in resources influences size primarily through changes in cell number while temperature acts through cell size. The difference in cellular mechanism may also explain the differences in growth trajectories resulting from food and temperature manipulations. There is, however, a poorly recognized interaction between food and temperature effects that needs further study. In addition, flies show a sexual dimorphism in temperature effects with the larger sex responding by changes in cell size and the smaller sex showing changes in both cell size and number. Leaf size is more variable than other organs, but there appears to be a consistent difference between how shade-tolerant and shade-intolerant species respond to light level. The former have larger leaves via cell size under shade, the latter via cell number in light conditions. Genetic differences, primarily from comparisons of D. melanogaster, show similar variation. Direct selection on body size alters cell number only, while temperature selection results in increased cell size and decreased cell number. Population comparisons along latitudinal clines show that larger flies have both larger cells and more cells. Use of these proximate patterns can give clues as to how selection acts in the wild. For example, the latitudinal pattern in D. melanogaster is usually assumed to be due to temperature, but the cellular pattern does not match that seen in laboratory selection at different temperatures. 相似文献
220.
The success of molecular research and its applications in both the clinical and basic research arenas is strongly dependent
on the collection, handling, storage, and quality control of fresh human tissue samples. This tissue bank was set up to bank
fresh surgically obtained human tissue using a Clinical Annotated Tissue Database (CATD) in order to capture the associated
patient clinical data and demographics using a one way patient encryption scheme to protect patient identification. In this
study, we determined that high quality of tissue samples is imperative for both genomic and proteomic molecular research.
This paper also contains a brief compilation of the literature involved in the patient ethics, patient informed consent, patient
de-identification, tissue collection, processing, and storage as well as basic molecular research generated from the tissue
bank using good clinical practices. The current applicable rules, regulations, and guidelines for handling human tissues are
briefly discussed. More than 6,610 cancer patients have been consented (97% of those that were contacted by the consenter)
and 16,800 tissue specimens have been banked from these patients in 9 years. All samples collected in the bank were QC’d by
a pathologist. Approximately 1,550 tissue samples have been requested for use in basic, clinical, and/or biomarker cancer
research studies. Each tissue aliquot removed from the bank for a research study were evaluated by a second H&E, if the samples
passed the QC, they were submitted for genomic and proteomic molecular analysis/study. Approximately 75% of samples evaluated
were of high histologic quality and used for research studies. Since 2003, we changed the patient informed consent to allow
the tissue bank to gather more patient clinical follow-up information. Ninety two percent of the patients (1,865 patients)
signed the new informed consent form and agreed to be re-contacted for follow-up information on their disease state. In addition,
eighty five percent of patients (1,584) agreed to be re-contacted to provide a biological fluid sample to be used for biomarker
research. 相似文献