全文获取类型
收费全文 | 16350篇 |
免费 | 727篇 |
国内免费 | 1564篇 |
专业分类
林业 | 1154篇 |
农学 | 1347篇 |
基础科学 | 2094篇 |
2446篇 | |
综合类 | 6657篇 |
农作物 | 832篇 |
水产渔业 | 374篇 |
畜牧兽医 | 2151篇 |
园艺 | 461篇 |
植物保护 | 1125篇 |
出版年
2024年 | 120篇 |
2023年 | 326篇 |
2022年 | 557篇 |
2021年 | 586篇 |
2020年 | 590篇 |
2019年 | 725篇 |
2018年 | 400篇 |
2017年 | 646篇 |
2016年 | 909篇 |
2015年 | 710篇 |
2014年 | 997篇 |
2013年 | 995篇 |
2012年 | 1464篇 |
2011年 | 1221篇 |
2010年 | 951篇 |
2009年 | 939篇 |
2008年 | 749篇 |
2007年 | 847篇 |
2006年 | 757篇 |
2005年 | 540篇 |
2004年 | 466篇 |
2003年 | 416篇 |
2002年 | 316篇 |
2001年 | 306篇 |
2000年 | 254篇 |
1999年 | 229篇 |
1998年 | 219篇 |
1997年 | 188篇 |
1996年 | 153篇 |
1995年 | 169篇 |
1994年 | 163篇 |
1993年 | 124篇 |
1992年 | 127篇 |
1991年 | 105篇 |
1990年 | 88篇 |
1989年 | 76篇 |
1988年 | 71篇 |
1987年 | 39篇 |
1986年 | 18篇 |
1985年 | 11篇 |
1984年 | 19篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 7篇 |
1977年 | 9篇 |
1973年 | 2篇 |
1955年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
试验表明,三道湾水电站原设计存在以下问题:泄洪排沙洞单独全开运行工况下,其进口上方存在贯通性吸气漏斗漩涡;正常溢洪洞进口侧收缩十分严重,泄流量不足,闸后存在水翅、折冲波等不良流态,下游消能效果不佳;针对实际情况,试验通过在泄洪排沙洞进口增设消涡格栅,在正常溢洪洞进口设置椭圆形导墙、延长闸后收缩段,下游采用扩散挑流消能等措施,很好地解决了上述问题。 相似文献
142.
明甪直天王殿松木斗拱振动台试验研究 总被引:2,自引:0,他引:2
以甪直保圣寺天王殿斗拱为参考对象,进行无缩尺松木斗拱模型的地震台试验研究。通过对斗拱的加速度与动力放大系数变化趋势、斗拱在振动过程中位移响应变化特征、斗拱变形最大时刻和各构件变形最大时刻的滑移位移和回转位移数值对比分析,得出以下结论:地震加速度用于衡量地震烈度,并不能直接反映斗拱试件的最大变形;振动频率的变化对斗拱回转变形的变化起重要作用,振幅是决定各构件水平滑移的主要因素;各构件变形最大值与斗拱整体变形最大值具有很强相关性,其中栌斗和华拱的回转变形对斗拱的整体变形而言,处于支配地位;斗拱的华拱连下昂部分主要起装饰作用,其榫卯连接节点位置在振动过程中较为薄弱,在对实际文物维护修缮过程中应引起重视并采取相关加固措施。 相似文献
143.
The influence of the structure and location of dam and weir on fluid flow state in a two-strand tundish is studied, and a set of optimal structure, combining with the average residence time calculated from RTD curve, is obtained. The result indicates that the fluid flow state can be changed and the path of the fluid flow can be prolonged as well as the average residence time is improved after using dam and weir. But there are some dead zones after fluid passed through the dam and weir. Combination scheme of No. one dam and weir is better than the others. Its average residence time is 299 s and the volume fraction of dead zone is 31.0%. After the optimization of flowing control parameters in tundish, the best case is that the distance between dam and weir is 290 mm and the distance between weir and the long nozzle is 383 mm. The longest average residence time is 351 s and the minimum volume fraction of dead zone is 19.0% under the above situation. Compared with that of no dam and weir, the average residence time increases by 65 s and the dead zone volume fraction decreases by 15.0%. Based on Newton formula, the calculated results show that the inclusions with diameter larger than 17.5 μm can float up within 351 s under this optimization situation. 相似文献
144.
145.
146.
The solution of polarization field strength in ellipsoid and a homogeneous dielectric in condition of a constant external field is obtained with strict derivation and ellipsoidal coordinate. The conclusion that some textbooks given: the direction of polarization field strength with the direction of external field holds strict anti-parallel must be supplemented with additive certain conditions, otherwise it will not be correct. By means of the latticework and the step change calculation, the angle value of polarization vector with the external field is calculated and the changing situation about the angle value with the change of three half axes of ellipsoid is analysied. 相似文献
147.
Xiang Dong 《保鲜与加工》1992,(6):98-105
A new scoap-like testability measure SCTM(a signal conflict oriented testability meaure) is presented, which represents not only the difficulty to control and observe the value of a node,but also the probability to cause signal conflict in the process of test generation. A parallel calculation scheme is offered, which speeds up the calculation m/2 times. Here m is the word length of a computer. 相似文献
148.
149.
According to Electrodynamics in curved spacetime, the interaction between gravitational waves (GW) and electromagnetic (EM) fields will produce perturbative electromagnetic fields. In a special EM system, namely, a Gaussian beam (Gb) propagating through a static magnetic field, the photon flux along the direction of the electric field of the Gb will be only a pure perturbative photon flux,when a GW propagates along the symmetric axis of a Gaussian beam. Detailed alanysis and calculation of the photon flux along several typical surfaces are performed, and a possible optimum plane which can receive perturbative photons up to 10~4s~(-1) is proposed. It is possible to provide an important method to detection of GW. 相似文献
150.