全文获取类型
收费全文 | 15486篇 |
免费 | 1746篇 |
国内免费 | 1127篇 |
专业分类
化学 | 13553篇 |
晶体学 | 37篇 |
力学 | 643篇 |
综合类 | 52篇 |
数学 | 349篇 |
物理学 | 3725篇 |
出版年
2024年 | 32篇 |
2023年 | 220篇 |
2022年 | 456篇 |
2021年 | 392篇 |
2020年 | 583篇 |
2019年 | 563篇 |
2018年 | 507篇 |
2017年 | 644篇 |
2016年 | 752篇 |
2015年 | 737篇 |
2014年 | 730篇 |
2013年 | 1055篇 |
2012年 | 1080篇 |
2011年 | 1031篇 |
2010年 | 830篇 |
2009年 | 956篇 |
2008年 | 903篇 |
2007年 | 932篇 |
2006年 | 853篇 |
2005年 | 748篇 |
2004年 | 696篇 |
2003年 | 598篇 |
2002年 | 457篇 |
2001年 | 363篇 |
2000年 | 335篇 |
1999年 | 274篇 |
1998年 | 236篇 |
1997年 | 179篇 |
1996年 | 173篇 |
1995年 | 164篇 |
1994年 | 150篇 |
1993年 | 103篇 |
1992年 | 97篇 |
1991年 | 88篇 |
1990年 | 70篇 |
1989年 | 58篇 |
1988年 | 45篇 |
1987年 | 36篇 |
1986年 | 30篇 |
1985年 | 34篇 |
1984年 | 28篇 |
1983年 | 17篇 |
1982年 | 29篇 |
1981年 | 23篇 |
1980年 | 11篇 |
1979年 | 12篇 |
1978年 | 16篇 |
1977年 | 5篇 |
1976年 | 13篇 |
1972年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
91.
We study elliptic systems of strongly nonlinear first-order differential equations in complex form on the plane. For such systems we develop the theory of Hilbert boundary value problems which is very much similar to the well-known theory for a holomorphic vector. Systems of nonlinear elliptic equations describe problems of interaction of several nonlinear stationary processes in the diffusive and convective mass and heat transport by hydrodynamic fluid flows. 相似文献
92.
93.
94.
95.
The effect of solar features on geospheric conditions leading to geomagnetic storms (GMSs) with planetary index,A
P ≥ 20 and the range of horizontal component of the Earth’s magnetic fieldH such that 250γ <H < 400γ has been investigated using interplanetary magnetic field (IMF), solar wind plasma (SWP) and solar geophysical data
(SGD) during the period 1978–99. Statistically, it is observed that maximum number of GMSs have occurred during the maximum
solar activity years of 21st and 22nd solar cycles. A peculiar result has been observed during the years 1982, 1994 when sunspot
numbers (SSNs) decrease very rapidly while numbers of GMSs increase. No distinct association between yearly occurrence of
disturbed days and SSNs is observed. Maximum number of disturbed days have occurred during spring and rainy seasons showing
a seasonal variation of disturbed days. No significant correlation between magnitude (intensity) of GMSs and importance ofH
α
, X-ray solar flares has been observed. Maximum number of GMSs is associated with solar flares of lower importance, i.e.,
SF during the period 1978-93.H
α
, X-ray solar flares occurred within lower helio-latitudes, i.e., (0–30)°N to (0–30)°S are associated with GMSs. NoH
α
, X-ray solar flares have occurred beyond 40°N or 40°S in association with GMSs. In helio-latitude range (10–40)°N to (10–40)°S,
the 89.5% concentration of active prominences and disappearing filaments (APDFs) are associated with GMSs. Maximum number
of GMSs are associated with solar flares. Coronal mass ejections (CMEs) are related with eruptive prominences, solar flares,
type IV radio burst and they occur at low helio-latitude. It is observed that CMEs related GMS events are not always associated
with high speed solar wind streams (HSSWSs). In many individual events, the travel time between the explosion on the Sun and
maximum activity lies between 58 and 118 h causing GMSs at the Earth. 相似文献
96.
《Magnetic resonance in chemistry : MRC》2003,41(2):139-142
Bioassay‐guided fractionation of the methanol extract of Odontadenia macrantha afforded a new limonoid, odontadenin A (1) and two known triterpenoids, lupeol (2) and α‐amyrin (3). The structure of 1 was established on the basis of 1D and 2D NMR and high‐resolution fast atom bombardment mass spectrometric data. The new compound was found to possess moderate cytotoxicity against A2780, the ovarian cancer cell line. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
97.
Using the multipoles method, we formulate the problems of radiation (both heave and sway) of water waves by a submerged sphere
in deep as well as in uniform finite depth water with an ice-cover, with the ice-cover being modelled as an elastic plate
of very small thickness. In each case this leads to an infinite system of linear equations which are solved numerically by
standard techniques. The added-mass and damping coefficients for a heaving and swaying sphere are obtained and depicted graphically
against the wave number for various values of the radius of the submerged sphere and flexural rigidity of the ice-cover to
show the effect of the presence of ice-cover on these quantities. When the flexural rigidity is taken to be zero, the numerical
results for the added-mass and damping coefficient for water with a free surface are recovered. 相似文献
98.
利用2~8 MeV的Naq+、Clq+(q=2,3,4,5)轰击氦原子,对碰撞的直接多重电离过程进行研究.实验采用反冲离子-散射离子飞行时间符合技术,通过反冲离子飞行时间谱区分不同价态反冲离子;利用静电偏转和位置灵敏探测技术区分不同电荷态散射离子;结合CAMAC-PC多参数获取系统得到一定价态散射离子所对应的反冲离子电荷态分布谱;经分析该谱得到直接多重电离截面与直接单电离截面之比R21.讨论了R21随入射离子速度和电荷态的变化关系. 相似文献
99.
Summary The potential of liquid chromatography-mass spectrometry (LC-MS) has been studied for the simultaneous determination of sixteen carbamate and organophosphorus pesticides in honeybees using a traditional sample preparation protocol based on acetone extraction and dichloromethane partitioning. The performances of both atmospheric pressure chemical ionization (APCI) and electrospray (ES) interfaces were compared. APCI offered better sensitivity and specificity for a higher range of pesticides. Limits of quantification were from 0.01 to 0.17 mg kg–1, at which recoveries obtained were between 64 and 93%, except for pirimicarb that was at 13%, with relative standard deviations ranging from 7 to 20%. Fenitrothion, fenoxycarb, methiocarb and phoxim were found in bees from Valencian Community beehives at concentrations between 0.03 and 3.75 mg kg–1. 相似文献
100.
Schwinger variational principle has been used to calculate triple differential cross-sections for ionization of hydrogen atoms
by positrons at intermediate and high energies for Ehrhardt type asymmetric geometry. The results agree in general with the
calculations of Brauneret al [8] and with the second Born calculation. 相似文献