全文获取类型
收费全文 | 1149篇 |
免费 | 62篇 |
专业分类
1211篇 |
出版年
2022年 | 12篇 |
2021年 | 21篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 27篇 |
2017年 | 14篇 |
2016年 | 33篇 |
2015年 | 43篇 |
2014年 | 51篇 |
2013年 | 65篇 |
2012年 | 107篇 |
2011年 | 81篇 |
2010年 | 49篇 |
2009年 | 50篇 |
2008年 | 63篇 |
2007年 | 42篇 |
2006年 | 67篇 |
2005年 | 49篇 |
2004年 | 46篇 |
2003年 | 26篇 |
2002年 | 44篇 |
2001年 | 22篇 |
2000年 | 11篇 |
1999年 | 10篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1995年 | 9篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 4篇 |
1975年 | 4篇 |
1971年 | 5篇 |
1956年 | 3篇 |
1936年 | 3篇 |
1929年 | 4篇 |
1928年 | 6篇 |
1919年 | 6篇 |
1918年 | 3篇 |
1913年 | 3篇 |
1851年 | 10篇 |
排序方式: 共有1211条查询结果,搜索用时 15 毫秒
81.
Male investment in testes and sperm duct gland in the polygamous nest breeding
two-spotted goby Gobiusculus flavescens (Fabricius) was
investigated in relation to time in reproductive season and individual physical
parameters. This small teleost fish is most likely the most abundant species
found along the rocky shores of the North East Atlantic. The two-spotted goby
has a single reproductive season, during which nest-caring males can raise
several clutches of offspring. According to the literature the males are on
average larger than the females. Here we report for the first time a population
showing a reversal of this trend, with males on average being smaller than
females, a difference likely caused by a large proportion of small males. Early
in the breeding season these small males have typical sneaker characters, with
relatively large testes and small seminal duct glands compared to the larger
dominant territorial males. The presence of these two alternative male
reproductive tactics is confirmed by histological studies, which shows the
presence of sperm in the sperm duct glands (SDG) of smaller males, but not in
the SDG of intermediate and larger males. To our knowledge, males with typical
sneaker characters have not been reported in earlier studied populations of
two-spotted goby. Interestingly we found that testes investment declined
significantly over the course of the breeding season, and that this reduction
was significantly more pronounced in small compared to the large males. Further,
a significant increase in seminal duct gland (SDG) mass was observed for the
smaller males over the breeding season. We propose that this indicates a
possible shift in mating tactic by smaller males from a parasitic to a
nest-holding tactic over the course of the breeding season. Thus, the observed
size dependent plasticity in investment in SDG over time suggests that the
reproductive tactic of G. flavescens is
conditional, and possibly influenced by mate availability and male—male
competition. 相似文献
82.
Rupert Seidl Werner Rammer Panagiotis Bellos Eduard Hochbichler Manfred J. Lexer 《Trees - Structure and Function》2010,24(1):139-150
The allocation of carbohydrates from photosynthesis to various plant compartments is a key process in ecophysiology and consequently
an important element in process-based ecosystem modeling. In this study, we tested generalized empirical equations in a widely
applied partitioning concept based on compartment-specific biomass allometries. For an 88-year chronosequence of European
beech (Fagus sylvatica L.) in Austria, we used the individual-based hybrid forest model PICUS v1.4 to compare simulations employing foliage biomass
functions at different levels of generalization against runs with site-specific parameterization and observations. Sensitivities
of the individual tree model were generally in line with the original stand-level partitioning concept and ecological process
understanding. While stand-level leaf area increased with increasing allocation to foliage, net primary productivity showed
no significant response due to saturated radiation interception in the dense chronosequence stands. Strong sensitivities were
revealed at the individual tree level, where favoring allocation to the foliage compartment resulted in increasing asymmetry
of competition and height–diameter relationships. Applying a generalized parameterization based on data from the full range
of continental species distribution resulted in a significant overestimation of mean tree height and subsequently standing
volume stock at the chronosequence. At a lower hierarchical level of generality, however, simulations with a representative
regional parameterization performed satisfactorily compared to model runs using the site-specific allometry. In relation to
common accuracy demands, e.g., in forest management decision support, the study suggests the rejection of a generic parameterization
while corroborating the use of regional generalizations in ecosystem models. 相似文献
83.
Sergei A. Bobrovnik Miroslava Demchenko Sergei Komisarenko Fred Stevens 《Journal of molecular recognition : JMR》2010,23(5):448-456
Traditionally used methods of antibody affinity determination either by ELISA or by the surface plasmon resonance technique do not allow detection of the presence of low‐affinity antibodies in samples of high‐affinity antibodies. In this paper we demonstrate the possibility to reveal their presence and to determine the affinities of both categories of antibodies as well as the ratio of their concentrations. This is especially important since by using traditional methods for antibody affinity evaluation the admixture of low‐affinity antibodies in a sample diminishes the accuracy in determination of specific antibody affinity. In addition, the presence of an admixture of low‐affinity antibodies may be an important biological characteristic of the system under study; their revelation and the evaluation of their binding parameters may be valuable in many cases for obtaining a more complete characterization of the binding properties of the multiple antibodies generated in an immune response. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
84.
Cashman JR MacDonald M Ghirmai S Okolotowicz KJ Sergienko E Brown B Garcia X Zhai D Dahl R Reed JC 《Bioorganic & medicinal chemistry letters》2010,20(22):6560-6564
High-throughput screening of 66,000 compounds using competitive binding of peptides comprising the BH3 domain to anti-apoptotic Bfl-1 led to the identification of 14 validated 'hits' as inhibitors of Bfl-1. N-Aryl maleimide 1 was among the validated 'hits'. A chemical library encompassing over 280 analogs of 1 was prepared following a two-step synthesis. Structure-activity studies for inhibition of Bfl-1 by analogs of N-aryl maleimide 1 revealed a preference for electron-withdrawing substituents in the N-aryl ring and hydrophilic amines appended to the maleimide core. Inhibitors of Bfl-1 are potential development candidates for anti-cancer therapeutics. 相似文献
85.
Structure of pyrimidine 5'-nucleotidase type 1. Insight into mechanism of action and inhibition during lead poisoning 总被引:1,自引:0,他引:1
Bitto E Bingman CA Wesenberg GE McCoy JG Phillips GN 《The Journal of biological chemistry》2006,281(29):20521-20529
Eukaryotic pyrimidine 5'-nucleotidase type 1 (P5N-1) catalyzes dephosphorylation of pyrimidine 5'-mononucleotides. Deficiency of P5N-1 activity in red blood cells results in nonspherocytic hemolytic anemia. The enzyme deficiency is either familial or can be acquired through lead poisoning. We present the crystal structure of mouse P5N-1 refined to 2.35 A resolution. The mouse P5N-1 has a 92% sequence identity to its human counterpart. The structure revealed that P5N-1 adopts a fold similar to enzymes of the haloacid dehydrogenase superfamily. The active site of this enzyme is structurally highly similar to those of phosphoserine phosphatases. We propose a catalytic mechanism for P5N-1 that is also similar to that of phosphoserine phosphatases and provide experimental evidence for the mechanism in the form of structures of several reaction cycle states, including: 1) P5N-1 with bound Mg(II) at 2.25 A, 2) phosphoenzyme intermediate analog at 2.30 A, 3) product-transition complex analog at 2.35 A, and 4) product complex at 2.1A resolution with phosphate bound in the active site. Furthermore the structure of Pb(II)-inhibited P5N-1 (at 2.35 A) revealed that Pb(II) binds within the active site in a way that compromises function of the cationic cavity, which is required for the recognition and binding of the phosphate group of nucleotides. 相似文献
86.
Distribution,phosphorylation, and activities of Hsp25 in heat-stressed H9c2 myoblasts: a functional link to cytoprotection 下载免费PDF全文
Bryantsev AL Loktionova SA Ilyinskaya OP Tararak EM Kampinga HH Kabakov AE 《Cell stress & chaperones》2002,7(2):146-155
The behavior of the endogenous heat shock protein 25 (Hsp25) in heat-stressed rat H9c2 myoblasts was studied. After mild or severe heating, this protein became less extractable with Triton X-100 and displayed characteristic immunofluorescence patterns, namely (1) granules in the nucleus, and (2) association with F-actin bundles in the cytoplasm. The intranuclear granulation of Hsp25 and its association with F-actin were sensitive to drugs affecting Hsp25 phosphorylation (cantharidin, sodium orthovanadate, SB203580, SB202190). Isoform analysis of Hsp25 translocated to the nucleus-free cytoskeletal fraction revealed only mono- and biphosphorylated Hsp25 and no unphosphorylated Hsp25. Transfected luciferase with initial localization in the nucleosol became colocalized with the Hsp25-containing granules after a heat shock treatment that denatured the enzyme in the cells. The association of Hsp25 with actin filaments after a mild heat stress conferred protection from subsequent F-actin-damaging treatments with cytochalasins (D and B) or severe heat stress. We hypothesize that (1) the binding of heat-denatured nucleosolic proteins to the Hsp25 contained in specific granular structures may serve for the subsequent chaperoning or degradation of the bound proteins, and (2) the actin cytoskeleton is stabilized by the direct targeting of phosphorylated Hsp25 to microfilament bundles. 相似文献
87.
Kalocayova Barbora Snurikova Denisa Vlkovicova Jana Navarova-Stara Veronika Michalikova Dominika Ujhazy Eduard Gasparova Zdenka Vrbjar Norbert 《Molecular and cellular biochemistry》2021,476(12):4323-4330
Molecular and Cellular Biochemistry - Previously it was shown that for reduction of anxiety and stress of experimental animals, preventive handling seems to be one of the most effective methods.... 相似文献
88.
89.
90.
Komlavi Anani Afanou Anne Straumfors Asbj?rn Skogstad Terje Nilsen Ole Synnes Ida Skaar Linda Hjeljord Arne Tronsmo Brett James Green Wijnand Eduard 《Applied and environmental microbiology》2014,80(22):7122-7130
Submicronic particles released from fungal cultures have been suggested to be additional sources of personal exposure in mold-contaminated buildings. In vitro generation of these particles has been studied with particle counters, eventually supplemented by autofluorescence, that recognize fragments by size and discriminate biotic from abiotic particles. However, the fungal origin of submicronic particles remains unclear. In this study, submicronic fungal particles derived from Aspergillus fumigatus, A. versicolor, and Penicillium chrysogenum cultures grown on agar and gypsum board were aerosolized and enumerated using field emission scanning electron microscopy (FESEM). A novel bioaerosol generator and a fungal spores source strength tester were compared at 12 and 20 liters min−1 airflow. The overall median numbers of aerosolized submicronic particles were 2 × 105 cm−2, 2.6 × 103 cm−2, and 0.9 × 103 cm−2 for A. fumigatus, A. versicolor, and P. chrysogenum, respectively. A. fumigatus released significantly (P < 0.001) more particles than A. versicolor and P. chrysogenum. The ratios of submicronic fragments to larger particles, regardless of media type, were 1:3, 5:1, and 1:2 for A. fumigatus, A. versicolor, and P. chrysogenum, respectively. Spore fragments identified by the presence of rodlets amounted to 13%, 2%, and 0% of the submicronic particles released from A. fumigatus, A. versicolor, and P. chrysogenum, respectively. Submicronic particles with and without rodlets were also aerosolized from cultures grown on cellophane-covered media, indirectly confirming their fungal origin. Both hyphae and conidia could fragment into submicronic particles and aerosolize in vitro. These findings further highlight the potential contribution of fungal fragments to personal fungal exposure. 相似文献