全文获取类型
收费全文 | 3791篇 |
免费 | 380篇 |
国内免费 | 2篇 |
专业分类
4173篇 |
出版年
2022年 | 56篇 |
2021年 | 69篇 |
2020年 | 57篇 |
2019年 | 59篇 |
2018年 | 62篇 |
2017年 | 52篇 |
2016年 | 95篇 |
2015年 | 159篇 |
2014年 | 172篇 |
2013年 | 208篇 |
2012年 | 246篇 |
2011年 | 255篇 |
2010年 | 132篇 |
2009年 | 156篇 |
2008年 | 189篇 |
2007年 | 176篇 |
2006年 | 155篇 |
2005年 | 150篇 |
2004年 | 155篇 |
2003年 | 148篇 |
2002年 | 149篇 |
2001年 | 75篇 |
2000年 | 77篇 |
1999年 | 73篇 |
1998年 | 46篇 |
1997年 | 32篇 |
1996年 | 32篇 |
1995年 | 25篇 |
1994年 | 31篇 |
1993年 | 24篇 |
1992年 | 57篇 |
1991年 | 50篇 |
1990年 | 47篇 |
1989年 | 47篇 |
1988年 | 32篇 |
1987年 | 43篇 |
1986年 | 35篇 |
1985年 | 27篇 |
1984年 | 34篇 |
1983年 | 39篇 |
1982年 | 32篇 |
1981年 | 23篇 |
1980年 | 23篇 |
1979年 | 29篇 |
1978年 | 23篇 |
1977年 | 20篇 |
1976年 | 20篇 |
1975年 | 33篇 |
1974年 | 26篇 |
1973年 | 25篇 |
排序方式: 共有4173条查询结果,搜索用时 15 毫秒
101.
Kramer K Voss HP Grimbergen JA Mills PA Huetteman D Zwiers L Brockway B 《Laboratory animals》2000,34(3):272-280
This paper describes for the first time the possibility for recording the systolic pressure (SP), diastolic pressure (DP), and the mean arterial pressure (MAP) as well as the heart rate (HR) and locomotor activity (LA) in freely moving mice, using a commercially available telemetry and data acquisition system. The system comprises a new, small radio-telemetry transmitter implanted in the peritoneal cavity, a receiver board placed underneath the home cage, a multiplexer and a computer-based data acquisition system. The signals from the receiver were consolidated by the multiplexer and were stored and analysed by the computer. The telemetered pressure signals (absolute pressure) were corrected automatically for changes in atmospheric pressure measured by an ambient pressure monitor. The effects of implantation on animal behaviour, and, after the animals had recovered, the effects of handling on the SP, DP, MAP and HR were examined. The radio-telemetry system for recording the SP, DP, MAP and HR provides an accurate and reliable method for monitoring the direct effects of handling on SP, DP, MAP and HR. In addition, by using this new blood pressure (BP) transmitter, we maintain that BP measurements in freely moving mice are more efficient, reliable, and less labour-intensive than the measurement techniques described in the literature thus far. 相似文献
102.
Sophie Camilleri-Broët Holly Vanderwerff Elizabeth Caldwell David Hockenbery 《Experimental cell research》1998,239(2):277
Recent studies have shown that reduction in mitochondrial membrane potential (ΔΨm) and generation of reactive oxygen species are early events in apoptosis. In this study, we present two different models of apoptotic cell death, Chinese hamster ovary (CHO) cells treated with aphidicolin and dexamethasone-treated 2B4 T-cell hybridoma cells, which display opposing mitochondrial changes. CHO cells arrested at G1/S with aphidicolin have a progressive increase in mitochondria mass and number, assessed by flow cytometry and fluorescent microscopy with mitochondria-specific probes. The increase in mitochondrial mass was not accompanied by a gain in net cellular mitochondrial membrane potential, consistent with an accumulation of relatively depolarized mitochondria. Fluorescent microscopy demonstrated an increased content of low ΔΨmmitochondria in aphidicolin-treated CHO cells, but high ΔΨmmitochondria were also present and remained stable in number. Mitochondrial mass correlated with decreased clonogenicity of aphidicolin-treated CHO cells. Cycloheximide prevented both the proliferation of mitochondria and subsequent cell death. In contrast, dexamethasone treatment of 2B4 T-cell hybridoma cells caused a decrease in ΔΨmwithout mitochondrial proliferation. Cycloheximide and Bcl-2 overexpression inhibited the loss of ΔΨm, as well as apoptosis. In both models, cell death was associated with a decrease in mitochondrial potential relative to mitochondrial mass, suggesting that an accumulation of damaged or dysfunctional mitochondria had occurred. 相似文献
103.
104.
The polar acetone-soluble lipids of Halobacterium cutirubrum were found to contain (in addition to the previously reported vitamin MK-8 and retinal) neo-bacterioruberin U, bacterioruberin, monoanhydrobacterioruberin, bis-anhydrobacterioruberin, an isomer of geranylgeraniol (with one internal cis-isoprene residue), 2,3,-di-O-phytanyl-sn-glycerol and two unidentified polar isoprenoids. All compounds were isolated in pure form by column and thin-layer chromatography, quantitated and characterized by their visible, ultraviolet, infrared, proton magnetic resonance and mass spectra and the spectra of their acetyl or silyl derivatives and/or dehydrated products. 相似文献
105.
Summary. In case–control studies evaluating the classification accuracy of a marker, controls are often matched to cases with respect to factors associated with the marker and disease status. In contrast with matching in epidemiologic etiology studies, matching in the classification setting has not been rigorously studied. In this article, we consider the implications of matching in terms of the choice of statistical analysis, efficiency, and assessment of the incremental value of the marker over the matching covariates. We find that adjustment for the matching covariates is essential, as unadjusted summaries of classification accuracy can be biased. In many settings, matching is the most efficient covariate-dependent sampling scheme, and we provide an expression for the optimal matching ratio. However, we also show that matching greatly complicates estimation of the incremental value of the marker. We recommend that matching be carefully considered in the context of these findings. 相似文献
106.
Jeffrey B. Graham Donald L. Kramer Elpidio Pineda 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1977,122(3):295-310
Summary
Piabucina festae, a Central American stream fish, breathes air frequently, even in air saturated water, however, is not an obligate air breather. Without access to air, it can maintain routine
by aquatic respiration down to aP
wO2 of about 70 Torr which is its critical O2 tension (P
cO2, Fig. 5). Aerial respiration averages 10% of total
in air saturated water and 70% in hypoxic water (Fig. 4). At lowP
wO2 air breathing is more frequent (Fig. 1), and more O2 is utilized from each air breath (Table 3), and tidal volume may increase (Fig. 7). Vascularized respiratory compartments or cells (Fig. 6), located in the second chamber of the physostomus gas bladder, function for aerial respiration. In ventilation air is gulped and forced through a large pneumatic duct into the gas bladder, excess gas is then released through opercula. Inspiration always precedes expiration and tidal volume is small, keeping gas bladderP
O
2 low (Table 4). Major differences in the air breathing physiology ofP. festae and other species are its higherP
cO2, a low aerial
in normoxic water, even though air gulps are frequent, and its pattern of inhalation prior to expiration. The interrelationship and optimization of the three gas bladder functions (buoyancy, sound reception, and air breathing) inP. festae is discussed. Aerial respiration may have evolved secondarily to the gas bladder's function in buoyancy control. 相似文献
107.
Svenson KL Ahituv N Durgin RS Savage H Magnani PA Foreman O Paigen B Peters LL 《Journal of lipid research》2008,49(11):2452-2462
In an effort to discover new mouse models of cardiovascular disease using N-ethyl-N-nitrosourea (ENU) mutagenesis followed by high-throughput phenotyping, we have identified a new mouse mutation, C699Y, in the LDL receptor (Ldlr), named wicked high cholesterol (WHC). When WHC was compared with the widely used Ldlr knockout (KO) mouse, notable phenotypic differences between strains were observed, such as accelerated atherosclerotic lesion formation and reduced hepatosteatosis in the ENU mutant after a short exposure to an atherogenic diet. This loss-of-function mouse model carries a single base mutation in the Ldlr gene on an otherwise pure C57BL/6J (B6) genetic background, making it a useful new tool for understanding the pathophysiology of atherosclerosis and for evaluating additional genetic modifiers regulating hyperlipidemia and atherogenesis. Further investigation of genomic differences between the ENU mutant and KO strains may reveal previously unappreciated sequence functionality. 相似文献
108.
109.
Trevor W. Joyce John W. Durban Diane E. Claridge Charlotte A. Dunn Leigh S. Hickmott Holly Fearnbach Karin Dolan David Moretti 《Marine Mammal Science》2020,36(1):29-46
The vulnerability of beaked whales (Family: Ziphiidae) to intense sound exposure has led to interest in their behavioral responses to mid-frequency active sonar (MFAS, 3–8 kHz). Here we present satellite-transmitting tag movement and dive behavior records from Blainville's beaked whales (Mesoplodon densirostris) tagged in advance of naval sonar exercises at the Atlantic Undersea Test and Evaluation Center (AUTEC) in the Bahamas. This represents one of the largest samples of beaked whales individually tracked during sonar operations (n = 7). The majority of individuals (five of seven) were displaced 28–68 km after the onset of sonar exposure and returned to the AUTEC range 2–4 days after exercises ended. Modeled sound pressure received levels were available during the tracking of four individuals and three of those individuals showed declines from initial maxima of 145–172 dB re 1 μPa to maxima of 70–150 dB re 1 μPa following displacements. Dive behavior data from tags showed a continuation of deep diving activity consistent with foraging during MFAS exposure periods, but also suggested reductions in time spent on deep dives during initial exposure periods. These data provide new insights into behavioral responses to MFAS and have important implications for modeling the population consequences of disturbance. 相似文献
110.
van Raalte DH van Leeuwen N Simonis-Bik AM Nijpels G van Haeften TW Schafer SA Boomsma DI Kramer MH J Heine R Maassen JA Staiger H Machicao F Häring HU Slagboom PE Willemsen G de Geus EJ Dekker JM Fritsche A Eekhoff EM Diamant M 't Hart LM 《Diabetic medicine : a journal of the British Diabetic Association》2012,29(8):e211-e216