全文获取类型
收费全文 | 1386篇 |
免费 | 132篇 |
国内免费 | 42篇 |
出版年
2023年 | 14篇 |
2022年 | 37篇 |
2021年 | 52篇 |
2020年 | 19篇 |
2019年 | 42篇 |
2018年 | 33篇 |
2017年 | 17篇 |
2016年 | 23篇 |
2015年 | 49篇 |
2014年 | 52篇 |
2013年 | 60篇 |
2012年 | 59篇 |
2011年 | 69篇 |
2010年 | 34篇 |
2009年 | 23篇 |
2008年 | 44篇 |
2007年 | 41篇 |
2006年 | 52篇 |
2005年 | 34篇 |
2004年 | 35篇 |
2003年 | 35篇 |
2002年 | 39篇 |
2001年 | 32篇 |
2000年 | 41篇 |
1999年 | 35篇 |
1998年 | 20篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 19篇 |
1994年 | 13篇 |
1993年 | 14篇 |
1992年 | 27篇 |
1991年 | 14篇 |
1990年 | 14篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 22篇 |
1984年 | 21篇 |
1983年 | 19篇 |
1982年 | 13篇 |
1980年 | 13篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 18篇 |
1976年 | 19篇 |
1974年 | 24篇 |
1973年 | 13篇 |
1972年 | 15篇 |
1969年 | 11篇 |
1968年 | 14篇 |
排序方式: 共有1560条查询结果,搜索用时 280 毫秒
161.
162.
Mi-2/NuRD: multiple complexes for many purposes 总被引:11,自引:0,他引:11
163.
Lizabeth Bowen Brian Aldridge Kimberlee Beckmen Tom Gelatt Lorrie Rea Kathy Burek Ken Pitcher Jeffrey L. Stott 《EcoHealth》2006,3(2):109-113
Characterization of the polygenic and polymorphic features of the Steller sea lion major histocompatibility complex (MHC) provides an ideal window for evaluating immunologic vigor of the population and identifying emergence of new genotypes that reflect ecosystem pressures. MHC genotyping can be used to measure the potential immunologic vigor of a population. However, since ecosystem-induced changes to MHC genotype can be slow to emerge, measurement of differential expression of these genes can potentially provide real-time evidence of immunologic perturbations. MHC DRB genes were cloned and sequenced using peripheral blood mononuclear leukocytes derived from 10 Steller sea lions from Southeast Alaska, Prince William Sound, and the Aleutian Islands. Nine unique DRB gene sequences were represented in each of 10 animals. MHC DRB gene expression was measured in a subset of six sea lions. Although DRB in genomic DNA was identical in all individuals, relative levels of expressed DRB mRNA was highly variable. Selective suppression of MHC DRB genes could be indicative of geographically disparate environmental pressures, thereby serving as an immediate and sensitive indicator of population and ecosystem health. 相似文献
164.
Albart Coster John WM Bastiaansen Mario PL Calus Johan AM van Arendonk Henk Bovenhuis 《遗传、选种与进化》2010,42(1):9
The objective of this simulation study was to compare the effect of the number of QTL and distribution of QTL variance on the accuracy of breeding values estimated with genomewide markers (MEBV). Three distinct methods were used to calculate MEBV: a Bayesian Method (BM), Least Angle Regression (LARS) and Partial Least Square Regression (PLSR). The accuracy of MEBV calculated with BM and LARS decreased when the number of simulated QTL increased. The accuracy decreased more when QTL had different variance values than when all QTL had an equal variance. The accuracy of MEBV calculated with PLSR was affected neither by the number of QTL nor by the distribution of QTL variance. Additional simulations and analyses showed that these conclusions were not affected by the number of individuals in the training population, by the number of markers and by the heritability of the trait. Results of this study show that the effect of the number of QTL and distribution of QTL variance on the accuracy of MEBV depends on the method that is used to calculate MEBV. 相似文献
165.
Since 2006, the known distribution of Hemimysis anomala has greatly expanded in the Great Lakes ecosystem, with, to date, 45 sites of occurrence among 91 monitored sites, located
in four of the Great Lakes and the upper St. Lawrence River. By means of carbon and nitrogen stable isotopes, a first assessment
of the feeding ecology of Hemimysis was completed. The δ13C values of 18 individuals collected in Lake Erie (Port Mainland) on a single date (Sept. 23, 2008) ranged from −30.2 to −24.5‰,
indicating that Hemimysis could feed on multiple carbon sources including pelagic and littoral autochthonous and terrestrial carbon. In Lake Erie,
variation in δ13C was related to δ15N, indicating the importance of food source for determining the trophic position of Hemimysis. The δ15N signatures of individuals were strongly related to their C/N ratios, suggesting that variations in the nutritional value
of Hemimysis may depend on trophic position. Isotopic variation among individuals in Lake Erie was complemented by temporal variation
in Lake Ontario. Monthly changes (from June to December 2008) in carbon isotope signatures were observed and related to changes
in water temperature, highlighting the variations in the baseline prey signatures that fuel Hemimysis diets. The observed variation in stable isotope signatures occurring among individuals within a localized Hemimysis assemblage and temporally should be considered as a key design feature in further studies attempting to identify the possible
effects of Hemimysis on nearshore food webs in the Great Lakes. 相似文献
166.
Transcriptional link between blood and bone: the stem cell leukemia gene and its +19 stem cell enhancer are active in bone cells
下载免费PDF全文
![点击此处可从《Molecular and cellular biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
167.
We studied the effects of natural and/or experimental infections of West Nile virus (WNV) in five raptor species from July 2002 to March 2004, including American kestrels (Falco sparverius), golden eagles (Aquila chrysaetos), red-tailed hawks (Buteo jamaicensis), barn owls (Tyto alba), and great horned owls (Bubo virginianus). Birds were infected per mosquito bite, per os, or percutaneously by needle. Many experimentally infected birds developed mosquito-infectious levels of viremia (>10(5) WNV plaque forming units per ml serum) within 5 days postinoculation (DPI), and/ or shed virus per os or per cloaca. Infection of organs 15-27 days postinoculation was infrequently detected by virus isolation from spleen, kidney, skin, heart, brain, and eye in convalescent birds. Histopathologic findings varied among species and by method of infection. The most common histopathologic lesions were subacute myocarditis and encephalitis. Several birds had a more acute, severe disease condition represented by arteritis and associated with tissue degeneration and necrosis. This study demonstrates that raptor species vary in their response to WNV infection and that several modes of exposure (e.g., oral) may result in infection. Wildlife managers should recognize that, although many WNV infections are sublethal to raptors, subacute lesions could potentially reduce viability of populations. We recommend that raptor handlers consider raptors as a potential source of WNV contamination due to oral and cloacal shedding. 相似文献
168.
Ellison LE O'Shea TJ Wimsatt J Pearce RD Neubaum DJ Neubaum MA Bowen RA 《Journal of wildlife diseases》2006,42(4):849-852
Blood was collected from wild big brown bats (Eptesicus fuscus) with and without anesthesia in Fort Collins, Colorado in 2004 to assess the impacts of these procedures on short-term survival and 1-yr return rates. Short-term survival and 1-yr return rates after release were passively monitored using PIT tag detection hoops placed at selected buildings. Comparison of 14-day maximum likelihood survival estimates from bats not bled (142 adult females, 62 volant juveniles), and bats sampled for blood with anesthesia (96 adult females, 23 volant juveniles) and without anesthesia (112 adult females, 22 volant juveniles) indicated no adverse effects of either treatment (juveniles: chi(2) = 53.38, df = 41, P = 0.09; adults: chi(2) = 39.09, df = 44, P = 0.68). Return rates of bats one year after sampling were similar among adult female controls (75.4%, n = 142, 95% CI = 67.4-82.2%), females sampled for blood with anesthesia (83.0%, n = 112, 95% CI = 74.8-89.5%), and females sampled without anesthesia (87.5%, n = 96, 95% CI = 79.2-93.4%). Lack of an effect was also noted in 1-yr return rates of juvenile females. These data suggest that the use of anesthesia during sampling of blood has no advantages in terms of enhancement of survival in big brown bats. 相似文献
169.
Francis P Martinez DM Taghipour F Bowen BD Haynes CA 《Biotechnology and bioengineering》2006,95(6):1207-1217
Controlled shear affinity filtration (CSAF) is a novel integrated processing technology that positions a rotor directly above an affinity membrane chromatography column to permit protein capture and purification directly from cell culture. The conical rotor is intended to provide a uniform and tunable shear stress at the membrane surface that inhibits membrane fouling and cell cake formation by providing a hydrodynamic force away from and a drag force parallel to the membrane surface. Computational fluid dynamics (CFD) simulations are used to show that the rotor in the original CSAF device (Vogel et al., 2002) does not provide uniform shear stress at the membrane surface. This results in the need to operate the system at unnecessarily high rotor speeds to reach a required shear stress of at least 0.17 Pa at every radial position of the membrane surface, compromising the scale-up of the technology. Results from CFD simulations are compared with particle image velocimetry (PIV) experiments and a numerical solution for low Reynolds number conditions to confirm that our CFD model accurately describes the hydrodynamics in the rotor chamber of the CSAF device over a range of rotor velocities, filtrate fluxes, and (both laminar and turbulent) retentate flows. CFD simulations were then carried out in combination with a root-finding method to optimize the shape of the CSAF rotor. The optimized rotor geometry produces a nearly constant shear stress of 0.17 Pa at a rotational velocity of 250 rpm, 60% lower than the original CSAF design. This permits the optimized CSAF device to be scaled up to a maximum rotor diameter 2.5 times larger than is permissible in the original device, thereby providing more than a sixfold increase in volumetric throughput. 相似文献
170.
Apoptosis is a specific mode of programmed cell death (PCD), recognized by characteristic morphological and molecular changes. Here we present evidence for a non-apoptotic type of PCD in human MCF-7 breast carcinoma cells. We used TNF-alpha and tyrphostin AG213 to induce apoptotic and non-apoptotic cell death respectively in vitro. Microscopic and immunohistochemical studies, together with DNA analysis and flow cytometric analysis of p53 and bcl-2 oncogene expression, revealed some novel characteristics of non-apoptotic cell death. We show here for the first time some of the biochemical features of an experimentally induced non-apoptotic PCD and emphasize the distinct biochemical events leading to apoptotic and non-apoptotic PCD. 相似文献