全文获取类型
收费全文 | 4654篇 |
免费 | 246篇 |
国内免费 | 273篇 |
专业分类
5173篇 |
出版年
2023年 | 75篇 |
2022年 | 76篇 |
2021年 | 107篇 |
2020年 | 128篇 |
2019年 | 141篇 |
2018年 | 91篇 |
2017年 | 111篇 |
2016年 | 117篇 |
2015年 | 131篇 |
2014年 | 221篇 |
2013年 | 307篇 |
2012年 | 181篇 |
2011年 | 227篇 |
2010年 | 158篇 |
2009年 | 173篇 |
2008年 | 232篇 |
2007年 | 236篇 |
2006年 | 210篇 |
2005年 | 184篇 |
2004年 | 184篇 |
2003年 | 161篇 |
2002年 | 138篇 |
2001年 | 130篇 |
2000年 | 118篇 |
1999年 | 124篇 |
1998年 | 82篇 |
1997年 | 72篇 |
1996年 | 73篇 |
1995年 | 83篇 |
1994年 | 76篇 |
1993年 | 64篇 |
1992年 | 55篇 |
1991年 | 52篇 |
1990年 | 41篇 |
1989年 | 47篇 |
1988年 | 45篇 |
1987年 | 44篇 |
1986年 | 50篇 |
1985年 | 53篇 |
1984年 | 36篇 |
1983年 | 36篇 |
1982年 | 45篇 |
1981年 | 26篇 |
1980年 | 45篇 |
1979年 | 31篇 |
1978年 | 37篇 |
1977年 | 20篇 |
1976年 | 18篇 |
1975年 | 24篇 |
1972年 | 16篇 |
排序方式: 共有5173条查询结果,搜索用时 15 毫秒
131.
为探明秸秆还田量对黑土力学特性的影响,以典型黑土区未经开垦(高有机质低黏粒含量)以及耕作40年(低有机质高黏粒含量)的土壤为研究对象,在秸秆长度为15 mm条件下,采用室内固结和三轴剪切相结合的方法,通过压缩指数、回弹指数、黏聚力及内摩擦角的测定与分析,模拟研究了黑土压缩-回弹及抗剪切行为对不同小麦秸秆还田比例(0%、25%、50%、75%、100%)的响应规律.结果表明: 添加秸秆后黑土力学性能明显改善,以开垦多年有机质含量低的黑土改善效果更为显著.秸秆全量还田时,最不易被压缩且压实后恢复能力最强;秸秆50%还田时,土体抗剪强度最大;当秸秆还田比例为50%~100%时,黑土抗压与抗蚀效果较好. 相似文献
132.
133.
魔芋甘露寡糖是一种具有肠道菌群调节作用的新型食品添加剂.本研究首次通过酶解与有机溶剂沉淀法制备了低分子质量的甘露寡糖(聚合度2~7),并对这类寡糖进行了长期毒性与遗传毒性评价.在长期毒性试验中,以大鼠为实验对象,分低、中、高(2.25,5.25,7.50 g/kg)药物剂量组和阴性对照组,连续灌胃给药90天.一般状况观察、生化指标、血液学指标、病理学等与对照组比较均无显著性差异,而大体解剖观察发现,部分大鼠的肝脏与肾脏形态发生变化,但这些变化均在正常范围内,且其他各项指标差异均无统计学意义.此外,一系列实验包括小鼠骨髓微核实验、Ames试验、小鼠精子畸变试验均未发现低分子质量甘露寡糖有明显的遗传毒性.试验结果提示,本研究方法获得的低分子质量甘露寡糖在本实验条件下未发现长期毒性与遗传毒性. 相似文献
134.
135.
Various ionic and molecular activities in the extracellular environment are vital to plant cell physiological processes. A noninvasive microsensing system (NMS) based on either the scanning ion-selective electrode technique (SIET) or the scanning polarographic electrode technique (SPET) is able to obtain information regarding the transportation of various ions/molecules in intact samples under normal physiological conditions. The two-probe simultaneous test system (2STS) is an integrated system composed of SIET,SPET, and a Xu-Kunkel sampling protocol. In the present study, 2STS was able to simultaneously measure fluxes of H+ and O2 of the lily (Lilium Iongiflorum Thunb. cv. Ace) pollen tube while avoiding interference between the two probes. The results indicate that the proton fluxes were effluxes, whereas the oxygen fluxes were influxes, and they were closely correlated to each other surrounding the constitutive alkaline band region. Specifically, when the proton effluxes increased, the oxygen influxes also increased. Therefore,the hypothesis of condensed active mitochondria existing in the alkalized area of the pollen tube proposed by Hepler's group is supported. 相似文献
136.
137.
Joya E. Nahon Menno Hoekstra Vanessa van Harmelen Patrick C.N. Rensen Ko Willems van Dijk Sander Kooijman Miranda Van Eck 《生物化学与生物物理学报:疾病的分子基础》2019,1865(2):494-501
Objective
Proteoglycan 4 (Prg4) has emerged from human association studies as a possible factor contributing to weight gain, dyslipidemia and insulin resistance. In the current study, we investigated the causal role of Prg4 in controlling lipid and glucose metabolism in mice.Methods
Prg4 knockout (KO) mice and wild-type (WT) littermates were challenged with an obesogenic high-fat diet (45% of total calories as fat) for 16?weeks. To further stimulate the development of metabolic alterations, 10% fructose water was provided starting from week 13.Results
Prg4 deficiency only tended to reduce diet-induced body weight gain, but significantly improved glucose handling (AUC: ?29%; p?<?0.05), which was also reflected by a tendency towards a reduced HOMA-IR score (?49%; p?=?0.06 as compared to WT mice). This coincided with lower hepatic expression of glycolysis (Gck: ?30%; p?<?0.05) and lipogenesis (Acc: ?21%; p?<?0.05 and Scd1: ?38%; p?<?0.001) genes, which translated in significantly lower hepatic triglyceride levels (?56%; p?<?0.001) in Prg4 KO mice as compared to WT mice. Prg4 KO mice likely had lower glucose utilization by skeletal muscle as compared to WT mice, judged by a significant reduction in the genes Glut4 (?29%; p?<?0.01), Pfkm (?21%; p?<?0.05) and Hk2 (?39%; p?<?0.001). Moreover, Prg4 KO mice showed a favorable white adipose tissue phenotype with lower uptake of triglyceride-derived fatty acids (?46%; p?<?0.05) and lower gene expression of inflammatory markers Cd68, Mcp1 and Tnfα (?65%, ?81% and ?63%, respectively; p?<?0.01) than WT mice.Conclusion
Prg4 KO mice are protected from high-fat diet-induced glucose intolerance and fatty liver disease. 相似文献138.
According to the instantaneous growth rate (dN/dt) of E. coli CVCC249 growing in batch culture, the entire growth progress was distinguished into four phases: accelerating growth phase,
constant growth phase, decelerating growth phase and declining phase, in each of which obvious variation in physiological
and biochemical properties was detected, including total DNA, total protein, and MTT-dehydrogenase activity, etc., that led
to difference in their antibiotic susceptivity. Antibiotic susceptivity of the population sampled from each phase was tested
by Concentration-killing Curve (CKC) approach following the formula N=N
0/{1+exp[r·(x-BC
50)]}, showing as normal distribution at the individual cell level for an internal population, in which the median bactericidal
concentration BC
50 represents the mean level of susceptivity, while the bactericidal span BC
1−99=(2lnN
0)/r indicates the variation degree of the antibiotic susceptivity. Furthermore, tested by CKC approach, the antibiotic susceptivity
of E. coli CVCC249 population in each physiological phase to gentamicin or enoxacin was various: susceptivity of the population in the
constant growth phase and declining phase all increased compared with that in the accelerating growth phase for gentamicin
but declined for enoxacin. The primary investigations revealed that the physiological phase should be taken into account in
the context of antibiotic susceptivity and research into antimicrobial mechanism. However there are few reports concerned
with this study. Further research using different kinds of antibiotics with synchronized continuous culture of different bacterial
strains is required.
Supported by the Natural Science Foundation of Shandong Province, China (Grant No. Y2005C58), the Natural Key Technology R&D
Program of China (Grant No. 2006BAK02A03-6) and the Youth Scientific Research Foundation of Shandong Academy of Agricultural
Science (2005YQ035) 相似文献
139.
分析2015年至2019年辽宁省人民医院血培养分离菌的科室分布及耐药情况,为临床提供数据参考.利用Whonet5.6软件对2015年至2019年辽宁省人民医院血培养临床数据进行分析.血培养阳性率为12.3%,共分离病原菌1266株,其中革兰阴性菌546株、革兰阳性菌649株、真菌71株;革兰阴性菌主要为大肠埃希菌(Es... 相似文献
140.
The purpose of this study was to determine whether general fatigue induced by incremental maximal exercise test (IMET) affects gait stability and variability in healthy subjects. Twenty-two young healthy male subjects walked in a treadmill at preferred walking speed for 4 min prior (PreT) the test, which was followed by three series of 4 min of walking with 4 min of rest among them. Gait variability was assessed using walk ratio (WR), calculated as step length normalized by step frequency, root mean square (RMSratio) of trunk acceleration, standard deviation of medial-lateral trunk acceleration between strides (VARML), coefficient of variation of step frequency (SFCV), length (SLCV) and width (SWCV). Gait stability was assessed using margin of stability (MoS) and local dynamic stability (λs). VARML, SFCV, SLCV and SWCV increased after the test indicating an increase in gait variability. MoS decreased and λs increased after the test, indicating a decrease in gait stability. All variables showed a trend to return to PreT values, but the 20-min post-test interval appears not to be enough for a complete recovery. The results showed that general fatigue induced by IMET alters negatively the gait, and an interval of at least 20 min should be considered for injury prevention in tasks with similar demands. 相似文献