全文获取类型
收费全文 | 4969篇 |
免费 | 409篇 |
专业分类
5378篇 |
出版年
2023年 | 38篇 |
2022年 | 86篇 |
2021年 | 142篇 |
2020年 | 84篇 |
2019年 | 107篇 |
2018年 | 156篇 |
2017年 | 115篇 |
2016年 | 196篇 |
2015年 | 283篇 |
2014年 | 257篇 |
2013年 | 361篇 |
2012年 | 412篇 |
2011年 | 418篇 |
2010年 | 206篇 |
2009年 | 190篇 |
2008年 | 263篇 |
2007年 | 257篇 |
2006年 | 234篇 |
2005年 | 201篇 |
2004年 | 190篇 |
2003年 | 171篇 |
2002年 | 176篇 |
2001年 | 83篇 |
2000年 | 55篇 |
1999年 | 59篇 |
1998年 | 53篇 |
1997年 | 39篇 |
1996年 | 36篇 |
1995年 | 26篇 |
1994年 | 22篇 |
1993年 | 17篇 |
1992年 | 25篇 |
1991年 | 33篇 |
1990年 | 31篇 |
1989年 | 16篇 |
1988年 | 14篇 |
1987年 | 22篇 |
1986年 | 21篇 |
1985年 | 25篇 |
1984年 | 25篇 |
1983年 | 29篇 |
1982年 | 20篇 |
1981年 | 19篇 |
1979年 | 24篇 |
1978年 | 16篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1974年 | 17篇 |
1973年 | 12篇 |
1968年 | 12篇 |
排序方式: 共有5378条查询结果,搜索用时 0 毫秒
991.
Laura Scillitani Gaëlle Darmon Andrea Monaco Giampaolo Cocca Enrico Sturaro Luca Rossi Maurizio Ramanzin 《The Journal of wildlife management》2013,77(4):761-769
The adaptation of translocated organisms to a new environment in the first years after their release is crucial in translocation programs because it may affect survival and reproductive success. Therefore, identifying the factors determining resource selection by the relocated animals is essential to improve the planning and the outcome of such programs. Using data collected in 2006–2009 in the framework of a restocking program, we studied the temporal variation of habitat selection in 14 translocated Alpine ibex (Capra ibex) during the year of their release and the following 3 years. We hypothesized a progressive adaptation of the translocated individuals, highlighted by a gradual decrease in the dissimilarities between translocated and resident individuals in ecological characteristics and social behavior. We tested the differences in habitat selection and home range size between the translocated and resident individuals and compared the spatial overlap between the groups. As expected, the dissimilarities decreased annually. The translocated and resident ibex almost immediately selected the same habitat resources, but the translocated individuals required 3 years to become fully socially assimilated. Our results indicated that habitat selection by gregarious species in a new environment is primarily driven by specific ecological requirements and that sociality plays a significant role. The translocated individuals tended to colonize areas already occupied by residents, either to fulfill social requirements and/or because the location of resident individuals may indicate high-quality habitat. This pattern of behavior must be considered in the planning of translocation programs because habitat selection can affect the outcomes of the programs. © 2013 The Wildlife Society. 相似文献
992.
Katrin Schmidt Antony J. Birchill Angus Atkinson Robert J. W. Brewin James R. Clark Anna E. Hickman David G. Johns Maeve C. Lohan Angela Milne Silvia Pardo Luca Polimene Tim J. Smyth Glen A. Tarran Claire E. Widdicombe E. Malcolm S. Woodward Simon J. Ussher 《Global Change Biology》2020,26(10):5574-5587
Continental margins are disproportionally important for global primary production, fisheries and CO2 uptake. However, across the Northeast Atlantic shelves, there has been an ongoing summertime decline of key biota—large diatoms, dinoflagellates and copepods—that traditionally fuel higher tropic levels such as fish, sea birds and marine mammals. Here, we combine multiple time series with in situ process studies to link these declines to summer nutrient stress and increasing proportions of picophytoplankton that can comprise up to 90% of the combined pico‐ and nanophytoplankton biomass in coastal areas. Among the pico‐fraction, it is the cyanobacterium Synechococcus that flourishes when iron and nitrogen resupply to surface waters are diminished. Our field data show how traits beyond small size give Synechococcus a competitive edge over pico‐ and nanoeukaryotes. Key is their ability to grow at low irradiances near the nutricline, which is aided by their superior light‐harvesting system and high affinity to iron. However, minute size and lack of essential biomolecules (e.g. omega‐3 polyunsaturated fatty acids and sterols) render Synechococcus poor primary producers to sustain shelf sea food webs efficiently. The combination of earlier spring blooms and lower summer food quantity and quality creates an increasing period of suboptimal feeding conditions for zooplankton at a time of year when their metabolic demand is highest. We suggest that this nutrition‐related mismatch has contributed to the widespread, ~50% decline in summer copepod abundance we observe over the last 60 years. With Synechococcus clades being prominent from the tropics to the Arctic and their abundances increasing worldwide, our study informs projections of future food web dynamics in coastal and shelf areas where droughts and stratification lead to increasing nutrient starvation of surface waters. 相似文献
993.
In this paper, a reverse-phase high-performance liquid chromatographic method using a chemically modified electrode coupled with microdialysis was developed to study the effect of electromagnetic impulse (EMI) on monoamine neurotransmitter metabolism in nerve cells. To detect the monoamines and their metabolites, a poly (para-aminobenzoic acid) (P-pABA)-modified electrode was prepared. The modified electrode exhibited efficiently electrocatalytic oxidation for monoamines and their metabolites with relatively high sensitivity, stability, and long life. Nerve cells were primarily cultured. EMI was radiated to three experimental model nerve cells: (i) on mature nerve cells, (ii) on the culture medium, and (iii) on juvenile nerve cells for various periods of time. Then the levels of monoamines in the culture medium were detected by high-performance liquid chromatography-electrochemical detection. The data indicated that electromagnetic fields could influence neurotransmitter metabolism by direct effect on nerve cells or effect on the nutrient medium and that the effect was not only relevant with the length of radiation time, but also with the growing state of the nerve cells. 相似文献
994.
Flamini G Pardini M Morelli I Ertugrul K Dural H Bagci Y Kargioglu M 《Phytochemistry》2002,61(4):433-437
Three flavonoid glycosides were isolated and characterized, together with a further 13 substances belonging to various classes of compounds, in particular two phenolic acids, a coumarin, a sugar and nine flavonoids from the flowered aerial parts of Centaurea pseudoscabiosa subsp. pseudoscabiosa Boiss. et Buhse (Asteraceae). Some considerations about their evolutionary meaning are provided. 相似文献
995.
TPR proteins: the versatile helix 总被引:32,自引:0,他引:32
Tetratrico peptide repeat (TPR) proteins have several interesting properties, including their folding characteristics, modular architecture and range of binding specificities. In the past five years, many 3D structures of TPR domains have been solved, revealing at a molecular level the versatility of this basic fold. Here, we discuss the structure of TPRs and highlight the diversity of arrangements and functions that are associated with these ubiquitous domains. Genomic analyses of the distribution of TPR domains are presented along with implications for protein engineering. 相似文献
996.
997.
998.
Galante Yves M. Merlini Luca Silvetti Tiziana Campia Paola Rossi Bianca Viani Fiorenza Brasca Milena 《Applied microbiology and biotechnology》2018,102(11):4687-4702
Applied Microbiology and Biotechnology - New biomaterials from renewable sources and the development of “functionalized biopolymers” are fields of growing industrial interest. Plant... 相似文献
999.
Luca Salvatore De Santo Michele Torella Gianpaolo Romano Ciro Maiello Marianna Buonocore Ciro Bancone Alessandro Della Corte Nicola Galdieri Gianantonio Nappi Cristiano Amarelli 《PloS one》2015,10(5)
MethodsData on 362 consecutive recipients (mean age: 47.8±13.7, 20.2% female, 18.2% diabetics, 22.1% with previous cardiac operations, 27.6% hospitalized, 84.9±29.4 ml/min preoperative glomerular filtration rate) were analyzed using multivariable logistic regression modeling. Target outcomes were determinants of troponin release, early graft failure (EGF), acute kidney injury (AKI) and operative death.ResultsMean cTnI release measured 24 hours after transplant was 10.9±11.6 μg/L. Overall hospital mortality was 10.8%, EGF 10.5%, and AKI was 12.2%. cTnI release>10 μg/L proved an independent predictor of EGF (OR 2.2; 95% CI, 1.06–4.6) and AKI (OR 1.031; 95% CI, 1.001-1.064). EGF, in turn, proved a determinant of hospital mortality. Risk factors for cTnI>10 μg/L release were: status 2B (OR 0.35; 95% CI, 0.18-0.69, protective), duration of the ischemic period (OR 1.006; 95% CI, 1.001-1.011), previous cardiac operation (OR 2.9; 95% CI, 1.67-5.0), and left ventricular hypertrophy (OR 3.3; 95% CI, 1.9-5.6).ConclusionsMyocardial enzyme leakage clearly emerged as an epiphenomenon of more complicated clinical course. The complex interplay between surgical procedure features, graft characteristics and recipient end-organ function highlights cTnI release as a risk marker of graft failure and acute kidney injury. The search for optimal myocardial preservation is still an issue. 相似文献
1000.
Luca Valzania Patrizia Romani Ling Tian Sheng Li Valeria Cavaliere Francesco Pennacchio Giuseppe Gargiulo 《PloS one》2014,9(4)
Polydnaviruses are obligate symbionts integrated as proviruses in the genome of some ichneumonoid wasps that parasitize lepidopteran larvae. Polydnavirus free viral particles, which are injected into the host at oviposition, express virulence factors that impair immunity and development. To date, most studies have focused on the molecular mechanisms underpinning immunosuppression, whereas how viral genes disrupt the endocrine balance remains largely uninvestigated. Using Drosophila as a model system, the present report analyzes the function of a member of the ankyrin gene family of the bracovirus associated with Toxoneuron nigriceps, a larval parasitoid of the noctuid moth Heliothis virescens. We found that the TnBVank1 expression in the Drosophila prothoracic gland blocks the larval-pupal molt. This phenotype can be rescued by feeding the larvae with 20-hydroxyecdysone. The localization of the TnBVANK1 is restricted to the cytoplasm where it interacts with Hrs and Alix marked endosomes. Collectively, our data demonstrate that the TnBVANK1 protein acts as a virulence factor that causes the disruption of ecdysone biosynthesis and developmental arrest by impairing the vesicular traffic of ecdysteroid precursors in the prothoracic gland steroidogenic cells. 相似文献