全文获取类型
收费全文 | 81531篇 |
免费 | 929篇 |
国内免费 | 847篇 |
专业分类
化学 | 26786篇 |
晶体学 | 827篇 |
力学 | 6933篇 |
综合类 | 37篇 |
数学 | 32374篇 |
物理学 | 16350篇 |
出版年
2023年 | 101篇 |
2022年 | 79篇 |
2021年 | 134篇 |
2020年 | 195篇 |
2019年 | 169篇 |
2018年 | 10543篇 |
2017年 | 10339篇 |
2016年 | 6213篇 |
2015年 | 1018篇 |
2014年 | 456篇 |
2013年 | 582篇 |
2012年 | 4044篇 |
2011年 | 10764篇 |
2010年 | 5820篇 |
2009年 | 6227篇 |
2008年 | 6796篇 |
2007年 | 8908篇 |
2006年 | 396篇 |
2005年 | 1479篇 |
2004年 | 1684篇 |
2003年 | 2069篇 |
2002年 | 1112篇 |
2001年 | 350篇 |
2000年 | 398篇 |
1999年 | 253篇 |
1998年 | 278篇 |
1997年 | 224篇 |
1996年 | 280篇 |
1995年 | 178篇 |
1994年 | 150篇 |
1993年 | 145篇 |
1992年 | 103篇 |
1991年 | 97篇 |
1990年 | 90篇 |
1989年 | 83篇 |
1988年 | 85篇 |
1987年 | 82篇 |
1986年 | 76篇 |
1985年 | 70篇 |
1984年 | 59篇 |
1983年 | 39篇 |
1982年 | 48篇 |
1981年 | 49篇 |
1980年 | 53篇 |
1979年 | 48篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
151.
R Ehrhardt 《The Journal of the Operational Research Society》1997,48(10):1013-1021
We consider a firm that manages its internal manufacturing operations according to a just-in-time (JIT) system but maintains an inventory of finished goods as a buffer against random demands from external customers. We formulate a model in which finished goods are replenished by a small fixed quantity each time period. In the interest of schedule stability, the size of the replenishment quantity must remain fixed for a predetermined interval of time periods. We analyse the single-interval problem in depth, showing how to compute a cost-minimising value of the replenishment quantity for a given interval length, and characterising the optimal cost, inventory levels and service as functions of the interval length and initial inventory. The model displays significant cost and service penalties for schedule stability. A dynamic version of the problem is also formulated, and shown to be convex in nature with relatively easily computed optima. 相似文献
152.
该文对Cd-HEDTA(N-(2-羟基乙基)乙二胺-N',N',N'-三乙酸),Cd-PDTA(1,2丙二胺四乙酸)和Cd-DTPA(二乙三胺五乙酸)的113Cd NMR谱和自旋晶格弛豫时间T1,及NOE因子进行了研究.结果表明,Cd-HEDTA和Cd-PDTA结构与Cd-EDTA类似,Cd-PDTA双线归因于其可能的两种异构体.Cd-DTPA大的化学位移表明其具有七配位的五角双锥结构.在这种结构中DTPA可用三个氮原子参加配位.对113Cd自旋晶格弛豫时间分析表明,Cd-DTPA配合物中质子偶极作用机理的贡献较大,这归因于Cd DTPA有更多的乙酸根亚甲基质子参与偶极作用. 相似文献
153.
Christian Prins 《The Journal of the Operational Research Society》1994,45(6):611-623
Satellite communications, like batches of work in a job shop, need to be scheduled in order to use their resources as efficiently as possible. The most common satellite communications system in use today is known as Time Division Multiple Access (TDMA), in which data from earth stations is buffered before being transmitted to the appropriate receiver on a satellite. Cycles of transmission are fixed for all stations. Since the same satellite will be used for routeing data in several different ways, a schedule must be devised to use the receivers, repeaters and transmitters on board to minimize the time needed for completion of a batch of work. This paper is a survey of current scheduling algorithms used for optimizing satellite communications resources. Apart from telecommunications, the methods presented here could be applied to more general scheduling problems with renewable resources but without precedence constraints. 相似文献
154.
A Pair of Dimeric Stilbene Epimers from Gnetum Montanum 总被引:1,自引:0,他引:1
GnetummontanumofgnetaceaisdistributedinsouthernChina.AsaChinesefOlkmedicine,itslianasareusedtotreatbronchitisandarthritis'.Previousinvestigationofthisspeciesledtotheisolationofsomealkaloidsanddibenzyletherde,i.ati.es2.lnourstudies,tenknowncomponentsincludingresveratrol,isohapontigenin,daucosterol,6-sitosterol,stearicacid,gnetifolinE,gnetol,isorhapontigenin-3-O-6-glucopyra(-)E-viniferinandgnetifolinCwereisolatedfromthesameresource.Atthesametime,apairoftraceepimerswereobtained.Thisisthefirste… 相似文献
155.
156.
157.
Vasily L. Morgunov 《Pramana》2007,69(6):1097-1100
A new calorimeter energy calibration method was developed for the proposed ILC detectors. The method uses the center-of-mass
energy of the accelerator as the reference. It has been shown that using the energy conservation law it is possible to make
ECAL and HCAL cross calibration to reach a good energy resolution for the simple calorimeter energy sum.
相似文献
158.
159.
Yong Nam Choi Shin Ae Kim Sung Kyu Kim Sung Baek Kim Chang-Hee Lee Pavel Mikula 《Pramana》2004,63(1):175-181
In a conventional diffractometer having single monochromator, only one position, parallel position, is used for the diffraction
experiment (i.e. detection) because the resolution property of the other one, anti-parallel position, is very poor. However,
a bent perfect crystal (BPC) monochromator at monochromatic focusing condition can provide a quite flat and equal resolution
property at both parallel and anti-parallel positions and thus one can have a chance to use both sides for the diffraction
experiment. From the data of the FWHM and the Δd/d measured on three diffraction geometries (symmetric, asymmetric compression and asymmetric expansion), we can conclude that
the simultaneous diffraction measurement in both parallel and anti-parallel positions can be achieved. 相似文献
160.
Forecasting electricity prices in presentday competitive electricity markets is a must for both producers and consumers because both need price estimates to develop their respective market bidding strategies. This paper proposes a transfer function model to predict electricity prices based on both past electricity prices and demands, and discuss the rationale to build it. The importance of electricity demand information is assessed. Appropriate metrics to appraise prediction quality are identified and used. Realistic and extensive simulations based on data from the PJM Interconnection for year 2003 are conducted. The proposed model is compared with naïve and other techniques. 相似文献