全文获取类型
收费全文 | 14307篇 |
免费 | 1191篇 |
国内免费 | 4篇 |
专业分类
15502篇 |
出版年
2023年 | 83篇 |
2022年 | 159篇 |
2021年 | 334篇 |
2020年 | 237篇 |
2019年 | 301篇 |
2018年 | 389篇 |
2017年 | 326篇 |
2016年 | 473篇 |
2015年 | 760篇 |
2014年 | 787篇 |
2013年 | 936篇 |
2012年 | 1165篇 |
2011年 | 1048篇 |
2010年 | 716篇 |
2009年 | 619篇 |
2008年 | 792篇 |
2007年 | 748篇 |
2006年 | 709篇 |
2005年 | 640篇 |
2004年 | 595篇 |
2003年 | 523篇 |
2002年 | 443篇 |
2001年 | 213篇 |
2000年 | 176篇 |
1999年 | 169篇 |
1998年 | 168篇 |
1997年 | 136篇 |
1996年 | 109篇 |
1995年 | 104篇 |
1994年 | 109篇 |
1993年 | 103篇 |
1992年 | 111篇 |
1991年 | 104篇 |
1990年 | 124篇 |
1989年 | 108篇 |
1988年 | 104篇 |
1987年 | 85篇 |
1986年 | 87篇 |
1985年 | 83篇 |
1984年 | 74篇 |
1983年 | 57篇 |
1982年 | 54篇 |
1981年 | 46篇 |
1980年 | 36篇 |
1979年 | 36篇 |
1978年 | 34篇 |
1977年 | 31篇 |
1976年 | 34篇 |
1975年 | 34篇 |
1973年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Violaine Garcia‐Fernandez Mathieu Amy André Lacroix Giorgio Malacarne Gérard Leboucher 《Ethology : formerly Zeitschrift fur Tierpsychologie》2010,116(7):662-670
Females invest differently in their eggs depending on the quality of their mates. In oscines, female investment is influenced by the quality of male song. In domestic canaries Serinus canaria, as well as in black‐capped chickadees Poecile atricapillus, females pay attention not only to the intrinsic quality of male song but can also gather information, by eavesdropping on male–male singing interactions, on the relative quality of males. During these interactions, overlapping the song of the rival is more threatening than alternating. Moreover eavesdropping female canaries have been shown to prefer the overlapping song rather than the overlapped song. The present study was designed to assess the effect of the information gathered by eavesdropping on female investment in eggs. First, we broadcasted overlapping interactions to female canaries. Then, we broadcasted to each female one of the two songs previously heard and collected eggs. Females exposed to overlapping songs laid eggs with greater yolk ratio than females exposed to overlapped songs. In contrast, yolk testosterone quantity and concentration were not affected by the treatment. Moreover, we found a variation between eggs with regard to the testosterone deposited in yolk: both quantity and concentration increased with laying order. Our results suggest that female canaries use information gathered by eavesdropping to differentially allocate resources into the eggs. They suggest that singing interactions could influence chick quality via female investment. 相似文献
992.
Diogo G. Garcia Lidia M. F. Amorim Mauro V. de Castro Faria Aline S. Freire Ricardo E. Santelli Clóvis O. Da Fonseca Thereza Quirico-Santos Patricia Burth 《Molecular and cellular biochemistry》2010,342(1-2):29-34
Indoleamine 2,3-dioxygenase (IDO) is an enzyme that suppresses adaptive T-cell immunity by catabolizing tryptophan from the cellular microenvironment. Inhibition of IDO pathway might enhance the efficacy of immunotherapeutic strategies for cancer. We synthesized 1-alkyl-tryptophan targeted IDO inhibitors and compared their effects on IDO expression and activity in dendritic cells (DCs) with the common IDO inhibitor 1-methyl-dl-tryptophan (1-MT). The IDO gene expression was examined by RT-PCR and realtime PCR. The toxicity of these analogs on the proliferation of DCs was detected by MTT assay. All of these analogs inhibited IDO expression and activity induced by IFN-γ and showed no cytotoxicity to DCs at 100 μM. 1-MT intensively suppressed IDO1 expression and activity in DCs, and 1-propyl-tryptophan (1-PT) and 1-isopropyl-tryptophan (1-isoPT) moderately inhibited them. 1-Butyl-tryptophan (1-BT) and 1-ethyl-tryptophan (1-ET) mainly inhibited IDO2 expression. Our results suggest that those analogs differed in their inhibitory activity on IDO expression may give us a clue for developing active IDO inhibitors. 相似文献
993.
We present an inventory of single or multiple calponin homology (CH) domain containing proteins of Dictyostelium discoideum. A multiple alignment and a phylogenetic tree of all 60 CH domains found in 36 proteins showed that most CH domains can be
assigned to one of 6 types. We have then distributed the proteins into several classes according to the type and arrangement
of the CH domains. Most proteins belong to the class of ABD (actin-binding domain)-forming CH tandems (CH1–CH2) of the α-actinin
and fimbrin families or to the class of CH3 domain-bearing proteins. There are a few examples of proteins with a single CH1
or CH2 domain, one with a CH1–CH1 doublet and a single representative of the CHe class of microtubule-binding proteins. A
comparison with CH domain proteins in Homo sapiens suggests that while the individual domains are available in both species, the existence of identical multidomain proteins
in toto is rare. Fimbrin 1, α-actinin and EB1 appear as perfect orthologs in both species, whereas filamin and interaptin
may represent ancestral forms of human filamin and nesprins. In four more cases (NAV/Unc-53-, smoothelin-, transgelin- and
Gas2-related proteins) functional data are needed in order to establish a potential relationship with a human counterpart.
Although extensive data exist for a few of the D. discoideum CH proteins, most remain to be characterized and our analysis may help predicting some of their properties. 相似文献
994.
995.
Paolo Ajmone‐Marsan Jos Fernando Garcia Johannes A. Lenstra 《Evolutionary anthropology》2010,19(4):148-157
Since their domestication in the Neolithic, cattle have belonged to our cultural heritage. The reconstruction of their history is an active field of research 1 that contributes to our understanding of human history. Archeological data are now supplemented by analyses of modern and ancient samples of cattle with DNA markers of maternal, paternal, or autosomal inheritance. The most recent genetic data suggest that maternal lineages of taurine cattle originated in the Fertile Crescent with a possible contribution of South‐European wild cattle populations, while zebu cattle originate from the Indus Valley. Subsequently, cattle accompanied human migrations, which led to the dispersal of domestic cattle of taurine, indicine, or mixed origin over Asia, Africa, Europe, and the New World. This has resulted in their adaptation to different environments and considerable variation in appearance and performance. More recently, rational management of breeding led to international movements of sires, which again changed the global patterns of genetic diversity. 相似文献
996.
Da Silva-Grigoletto ME Fernández JM de Sá CA Gómez-Puerto JR Vaamonde D Pérez-Jiménez F 《Journal of strength and conditioning research / National Strength & Conditioning Association》2010,24(12):3334-3342
The addition of fructose (F) to a glucose (G) supplement may modify the metabolic response during exercise; however, its effect on perceived exertion (PE) and its influence on postprandial metabolism have not been jointly studied in different types of exercise. This study sought to assess the acute effects of F addition to a G supplement on PE and on the postprandial metabolic response during a single bout of either strength exercise (SE) or endurance exercise (EE). Twenty physically trained men ingested an oral dose of G or GF 15 minutes before starting a 30-minute session of SE (10 sets of 10 repetitions of half squat) or EE (cycling). The combination resulted in 4 randomized interventions in a crossover design in which all subjects performed all experimental conditions: G + SE, GF + SE, G + EE, and GF + SE. Perceived exertion, heart rate (HR), G, insulin, lactate, and urinary catecholamine levels were measured before exercise, during the exercise, and during acute recovery. Perceived exertion during exercise was lower for GF than for G during SE and EE (mean ± SD; 8.95 ± 0.62 vs. 9.26 ± 0.65, p < 0.05 and 7.47 ± 0.84 vs. 7.74 ± 0.93, p < 0.05, respectively). The glycemic peak in GF + SE was lower than in G + SE (p < 0.05), and there was a second peak during recovery (p < 0.05), whereas in EE, no difference in blood G levels was noted between G and GF supplements. Moreover, HR, urinary adrenalin, and noradrenalin were lower in GF than in G (p < 0.05), though only for EE. The results showed that PE is positively affected by GF supplementation for both SE and EE and thus may be a useful dietary strategy for helping to achieve higher training loads. 相似文献
997.
998.
María Isabel Burgos Alves Francisco Avilés Plaza Rebeca Martínez-Tomás María Sánchez-Campillo Elvira Larqué Francisca Pérez-Llamas Pedro Martínez Hernández Soledad Parra Pallarés 《Journal of physiology and biochemistry》2010,66(3):221-227
The biological effects of oxidized LDL (oxLDL) may contribute to initiation and progression of the atherosclerotic process,
and the association between cardiovascular disease and oxidation of LDL has been largely demonstrated. The objectives of this
study were to establish the reference values of oxidative stress biomarkers in a young healthy Spanish population to determine
the concentration of oxLDL and its relationship with lipid profile and with these biomarkers. oxLDL, F2-isoprostanes, protein carbonyls (PC), and 8-hydroxy-2′-deoxyguanosine (8-OHdG) were determinate by ELISA in 72 healthy subjects.
Antioxidant enzymes, superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR) were carried
out on a Hitachi 912 analyzer; lipid profile were assayed using automated systems (Cobas 711, Roche Diagnostics). All statistics
were analyzed by using SPSS for Windows 15.0. SPSS Inc, Chicago, IL, USA. (Normal mean reference values): oxLDL (63.23 ± 16.23
U/L), (Male/Female 68.06 ± 17.69/58.39 ± 13.6 U/L), F2-isoprostanes (2.26 ± 0.9 μg/g creatinine), PC (0.34 ± 0.15 nmol/mg), 8-OHdG (23.27 ± 10.58 ng/ml), SOD (931.97 ± 271.09 U/g
Hb), GR (46.56 ± 11.68 U/L), GPx (27.58 ± 6.89 U/gHb (Male/Female 25.91 ± 5.03/29.2 ± 8.07 U/L)). OxLDL (63.23 U/L) was significantly
(p < 0.05) positively correlated with BMI (22.53 Kg/m2), total cholesterol (175.79 mg/dl), triglycerides (87.58 mg/dl), LDL cholesterol (96.25 mg/dl), and uric acid (4.78 mg/dl),
while negatively correlated with HDL-cholesterol (62.25 mg/dl). We have found different correlation between oxLDL and isoprostanes
by gender with the rest of parameters. Normal reference values have been found significantly different for oxLDL and GPx by
gender. Oxidized LDL is correlated with lipid profile but not with the oxidative stress biomarkers. Urinary isoprostanes are
positively correlated with triglycerides and negatively with GR and GPx. 相似文献
999.
Prakash Peddi Charles W. Loftin Jennifer S. Dickey Jessica M. Hair Kara J. Burns Khaled Aziz Dave C. Francisco Mihalis I. Panayiotidis Olga A. Sedelnikova William M. Bonner Thomas A. Winters Alexandros G. Georgakilas 《Free radical biology & medicine》2010,48(10):1435-1443
DNA-dependent protein kinase (DNA-PK) is a key non-homologous-end-joining (NHEJ) nuclear serine/threonine protein kinase involved in various DNA metabolic and damage signaling pathways contributing to the maintenance of genomic stability and prevention of cancer. To examine the role of DNA-PK in processing of non-DSB clustered DNA damage, we have used three models of DNA-PK deficiency, i.e., chemical inactivation of its kinase activity by the novel inhibitors IC86621 and NU7026, knockdown and complete absence of the protein in human breast cancer (MCF-7) and glioblastoma cell lines (MO59-J/K). A compromised DNA-PK repair pathway led to the accumulation of clustered DNA lesions induced by γ-rays. Tumor cells lacking protein expression or with inhibited kinase activity showed a marked decrease in their ability to process oxidatively induced non-DSB clustered DNA lesions measured using a modified version of pulsed-field gel electrophoresis or single-cell gel electrophoresis (comet assay). In all cases, DNA-PK inactivation led to a higher level of lesion persistence even after 24–72 h of repair. We suggest a model in which DNA-PK deficiency affects the processing of these clusters first by compromising base excision repair and second by the presence of catalytically inactive DNA-PK inhibiting the efficient processing of these lesions owing to the failure of DNA-PK to disassociate from the DNA ends. The information rendered will be important for understanding not only cancer etiology in the presence of an NHEJ deficiency but also cancer treatments based on the induction of oxidative stress and inhibition of cluster repair. 相似文献
1000.
We study the unbiased folding/unfolding thermodynamics of the Trp‐cage miniprotein using detailed molecular dynamics simulations of an all‐atom model of the protein in explicit solvent using the Amberff99SB force field. Replica‐exchange molecular dynamics simulations are used to sample the protein ensembles over a broad range of temperatures covering the folded and unfolded states at two densities. The obtained ensembles are shown to reach equilibrium in the 1 μs/replica timescale. The total simulation time used in the calculations exceeds 100 μs. Ensemble averages of the fraction folded, pressure, and energy differences between the folded and unfolded states as a function of temperature are used to model the free energy of the folding transition, ΔG(P, T), over the whole region of temperatures and pressures sampled in the simulations. The ΔG(P, T) diagram describes an ellipse over the range of temperatures and pressures sampled, predicting that the system can undergo pressure‐induced unfolding and cold denaturation at low temperatures and high pressures, and unfolding at low pressures and high temperatures. The calculated free energy function exhibits remarkably good agreement with the experimental folding transition temperature (Tf = 321 K), free energy, and specific heat changes. However, changes in enthalpy and entropy are significantly different than the experimental values. We speculate that these differences may be due to the simplicity of the semiempirical force field used in the simulations and that more elaborate force fields may be required to describe appropriately the thermodynamics of proteins. Proteins 2010. © 2010 Wiley‐Liss, Inc. 相似文献