全文获取类型
收费全文 | 1708篇 |
免费 | 16篇 |
国内免费 | 10篇 |
专业分类
林业 | 149篇 |
农学 | 362篇 |
基础科学 | 12篇 |
370篇 | |
综合类 | 266篇 |
农作物 | 97篇 |
水产渔业 | 14篇 |
畜牧兽医 | 394篇 |
园艺 | 6篇 |
植物保护 | 64篇 |
出版年
2024年 | 21篇 |
2023年 | 60篇 |
2022年 | 83篇 |
2021年 | 32篇 |
2020年 | 13篇 |
2019年 | 10篇 |
2018年 | 9篇 |
2017年 | 5篇 |
2016年 | 14篇 |
2015年 | 25篇 |
2014年 | 30篇 |
2013年 | 52篇 |
2012年 | 214篇 |
2011年 | 192篇 |
2010年 | 35篇 |
2009年 | 33篇 |
2008年 | 136篇 |
2007年 | 111篇 |
2006年 | 101篇 |
2005年 | 89篇 |
2004年 | 58篇 |
2003年 | 53篇 |
2002年 | 45篇 |
2001年 | 35篇 |
2000年 | 37篇 |
1999年 | 19篇 |
1998年 | 21篇 |
1997年 | 16篇 |
1996年 | 21篇 |
1995年 | 26篇 |
1994年 | 17篇 |
1993年 | 28篇 |
1992年 | 30篇 |
1991年 | 13篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 11篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1958年 | 1篇 |
排序方式: 共有1734条查询结果,搜索用时 15 毫秒
1.
2.
Yang QE Hou YP Zhou GB Yang ZQ Zhu SE 《The Journal of reproduction and development》2007,53(2):211-218
In the present study, mouse blastocysts were employed to investigate the feasibility and efficiency of stepwise in-straw dilution and direct transfer using the open pulled straw (OPS) method. In experiment I, the effects of various vitrification solutions (VS) on embryo survival were examined. After thawing, the expanded blastocyst rates (97.59 and 95.05%) and hatching rates (80.48 and 78.95%) achieved in the EDFS30 [15% ethylene glycol (EG), 15% dimethyl sulfoxide (DMSO), Ficoll, and sucrose] and EFS40 [40% EG, Ficoll, and sucrose] groups were no different from those (96.15% and 83.33%) of the control group. However, the rates in the EFS30 [30% EG, Ficoll, and sucrose] (87.80 and 55.43%) and EDFS40 [20% EG, 20% DMSO, Ficoll, and sucrose] (95.69 and 70.97%) groups were significantly lower than those (96.15 and 83.33%) of the control group (P<0.05). In the experiment II, the effects of the volume of VS in the OPS on the survival of embryos after in-straw thawing were investigated. When the length of the VS in the column was less than 1 cm, the in vitro viability of embryos thawed by stepwise in-straw dilution was no different among the experimental and control groups. The embryos could be successfully thawed by immersing the OPS in 0.5 M sucrose for 3 min and then 0.25 M sucrose for 2 min. In experiment III, the effect of immersion time of the OPS in diluent (PBS) on the viability of vitrified embryos was investigated. After in-straw thawing, OPSs were immersed immediately in 1 ml PBS for 0 to 30 min. When the immersion time of the OPSs in PBS was less than 12 min, in vitro development of the in-straw thawed embryos was no different from that of the controls. In experiment IV, in-straw thawed blastocysts were directly transferred to pseudopregnant mice to examine their in vivo developmental viability. The pregnancy (91.67%) and birth rates (42.42%) of embryos in-straw thawed and directly transferred were no different from those of the unvitrified controls (90.90 and 40%) and embryos thawed by the conventional method (84.61 and 46.94%). These results demonstrate that mouse embryos vitrified with OPS could be successfully thawed by stepwise in-straw dilution and transferred directly to a recipient and that this method might be a model for field manipulation of vitrified embryos in farm animals. 相似文献
3.
Yang Chunwei 《保鲜与加工》1988,(4)
This paper studies the tactics choice and its improvement in the development of economy by means of Markovian Decision Programming. An optimal decision and the maximum expected revenue can be obtained. The . paper also presents the procedures and formulas of numerical evaluation. 相似文献
4.
Sun Dihua Yang Yongzhen 《保鲜与加工》1991,(6):62-68
In order to improve the convergence rate of the algorithms, an acceleration search method along a straight or curve is proposed,and the specific calculation steps of the algorithms are presented. The numerical results in model parameter estimation show that the convergence rate is improved and the calculation accords with the practical demands. 相似文献
5.
According to the security investment theory of Markowitz,this paper presents aCaculation method of portfolio investment under the risk minimization,and some mathematic expres-sions of the efficient frontier for portfolio investment are conducted.Based on these,the efficientfrontier is proved as a parabola,and a practical caculation process is given. 相似文献
6.
Control Strategy and Simulation Study on NiMH Battery Quick Charging for Regenerative Braking of HEV
Based on the result of NiMH battery performance experiments, changing trend of maximal temperature and difference in temperature of HEV NiMH battery in different SOC and different charging current is analyzed. Considering the working situation of HEV NiMH battery and the theory of battery quick charging, a control strategy for NiMH battery quick charging is described which adapts to HEV regenerative braking system based on Mascc law. By Modeling and simulating the process of NiMH battery quick charging with this strategy, constant voltage charge method and constant current charge method, validates this control strategy. 相似文献
7.
Du Yang Xin Mingdao Huang Shaoming 《保鲜与加工》1995,(5):50-56
A new type of three dimenstional inner microfin tube is devoloped. Under four different pressures and in the range of condensing mass velocities from 33 to 153 kg/m2 . s,and by the experimental study of the three kinds of tubes with different microfin parameters, the performances of the condensation heat transfer for R11 in the horizontal microfin tubes and obtained. The experiments show that the inner microfin tube is a hopeful and nighty effective condensing heat transfer enhancement tube. 相似文献
8.
Yang Yudin Liu Dejun 《保鲜与加工》1990,(1):110-118
In this paper, taking a D1201 spindle as an example, we discuss the dynamic analysis of spindle by using the theory of the complex model, we also analyse the factors which effect the dynamic characterics of spindle and give results which arc reference value to improving the structure of spindle, 相似文献
9.
This paper introduces a method of solving the problem of leather cavity measurement in shoe CAD/CAM by industrial CT technology. Concentrating on peculiarity and requirement of leather cavity measurement, this paper presents a X-ray industrial CT system scheme, which not only satisfy the requirement of leather cavity measurement but also can achieve general industrial CT. measurement. The achievement on data collection system and motion control of stepping motor is emphasized. 相似文献
10.