全文获取类型
收费全文 | 83901篇 |
免费 | 451篇 |
国内免费 | 408篇 |
专业分类
化学 | 28340篇 |
晶体学 | 877篇 |
力学 | 6867篇 |
数学 | 32875篇 |
物理学 | 15801篇 |
出版年
2021年 | 49篇 |
2019年 | 64篇 |
2018年 | 10478篇 |
2017年 | 10292篇 |
2016年 | 6157篇 |
2015年 | 948篇 |
2014年 | 394篇 |
2013年 | 636篇 |
2012年 | 4027篇 |
2011年 | 10783篇 |
2010年 | 5759篇 |
2009年 | 6171篇 |
2008年 | 6853篇 |
2007年 | 9051篇 |
2006年 | 479篇 |
2005年 | 1600篇 |
2004年 | 1775篇 |
2003年 | 2250篇 |
2002年 | 1254篇 |
2001年 | 352篇 |
2000年 | 387篇 |
1999年 | 239篇 |
1998年 | 259篇 |
1997年 | 235篇 |
1996年 | 293篇 |
1995年 | 213篇 |
1994年 | 168篇 |
1993年 | 164篇 |
1992年 | 126篇 |
1991年 | 133篇 |
1990年 | 106篇 |
1989年 | 125篇 |
1988年 | 141篇 |
1987年 | 116篇 |
1986年 | 116篇 |
1985年 | 131篇 |
1984年 | 151篇 |
1983年 | 109篇 |
1982年 | 137篇 |
1981年 | 139篇 |
1980年 | 142篇 |
1979年 | 123篇 |
1978年 | 117篇 |
1977年 | 96篇 |
1976年 | 93篇 |
1975年 | 83篇 |
1974年 | 71篇 |
1973年 | 69篇 |
1972年 | 47篇 |
1914年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
As evidence for his conjecture in birational log geometry, Kawamata constructed a family of derived equivalences between toric
orbifolds. In a previous paper, the authors showed that the derived category of a toric orbifold is naturally identified with
a category of polyhedrally-constructible sheaves on ℝ
n
. In this paper we investigate and reprove some of Kawamata’s results from this perspective. 相似文献
972.
The factors affecting performance of fractured wells are analyzed in this work. The static and dynamic geologic data of fractured
well and fracturing treatment parameters obtained from 51 fractured wells in sand reservoirs of Zhongyuan oilfield are analyzed
by applying the grey correlation method. Ten parameters are screened, including penetrability, porosity, net thickness, oil
saturation, water cut, average daily production, and injection rate, amount cementing front spacer, amount sand-carrying agent
and amount sand. With the novel Radial Basis Function neural network model based on immune principles, 13 parameters of 42
wells out of 51 are used as the input samples and the stimulation ratios as the output samples. The nonlinear interrelationship
between the input samples and output samples are investigated, and a productivity prediction model of optimizing fracture
design is established. The data of the rest 7 wells are used to test the model. The results show that the relative errors
are all less than 7%, which proves that the novel Radial Basis Function neural network model based on immune principles has
less calculation, high precision and good generalization ability. 相似文献
973.
It is well known that any Vitali set on the real line ? does not possess the Baire property. The same is valid for finite unions of Vitali sets. What can be said about infinite unions of Vitali sets? Let S be a Vitali set, S r be the image of S under the translation of ? by a rational number r and F = {S r : r is rational}. We prove that for each non-empty proper subfamily F′ of F the union ∪F′ does not possess the Baire property. We say that a subset A of ? possesses Vitali property if there exist a non-empty open set O and a meager set M such that A ? O \ M. Then we characterize those non-empty proper subfamilies F′ of F which unions ∪F′ possess the Vitali property. 相似文献
974.
Vitaly Maiorov 《Advances in Computational Mathematics》2010,32(2):239-253
We study geometrical properties of the ridge function manifold \(\mathcal{R}_n\) consisting of all possible linear combinations of n functions of the form g(a· x), where a·x is the inner product in \({\mathbb R}^d\). We obtain an estimate for the ε-entropy numbers in terms of smaller ε-covering numbers of the compact class G n,s formed by the intersection of the class \(\mathcal{R}_n\) with the unit ball \(B\mathcal{P}_s^d\) in the space of polynomials on \({\mathbb R}^d\) of degree s. In particular we show that for n?≤?s d???1 the ε-entropy number H ε (G n,s,L q ) of the class G n,s in the space L q is of order nslog1/ε (modulo a logarithmic factor). Note that the ε-entropy number \(H_\varepsilon(B\mathcal{P}_s^d,L_q)\) of the unit ball is of order s d log1/ε. Moreover, we obtain an estimate for the pseudo-dimension of the ridge function class G n,s. 相似文献
975.
K Sheibani 《The Journal of the Operational Research Society》2010,61(5):813-818
This paper describes a polynomial-time heuristic for the permutation flow-shop scheduling problem with the makespan criterion. The proposed method consists of two phases: arranging the jobs in priority order and then constructing a sequence. A fuzzy greedy evaluation function is employed to prioritize the jobs for incorporating into the construction phase of the heuristic. Computational experiments using standard benchmark problems indicate an improvement of the new heuristic over the well-known Nawaz, Enscore and Ham (NEH) heuristic. It will be seen that the NEH heuristic is a special case of our more general heuristic. 相似文献
976.
Jesper L. Mortensen Alan McWilliam Christopher G. Leburn Peter Tidemand-Lichtenberg Morten Thorhauge Jirí Janousek Christian T.A. Brown Alexander A. Lagatsky Preben Buchhave Wilson Sibbett 《Optics Communications》2006,260(2):637-640
Efficient generation of continuous-wave (CW) tunable light in the yellow region is reported. The method is based on sum-frequency mixing of a tunable Cr4+:forsterite laser with a Nd:YVO4 laser. A periodically poled lithium niobate crystal was placed intra-cavity in a Nd:YVO4 laser, and the Cr4+:forsterite laser was single-passed through the non-linear media. With this setup, it was possible to generate up to 3 mW of yellow light smoothly tunable from 573 to 587 nm. This is the highest output demonstrated to date for a tunable diode pumped solid-state CW laser in this wavelength region. The ways to improve the efficiency further are discussed. 相似文献
977.
Lawrence W. Jones 《Czechoslovak Journal of Physics》2006,56(1):A201-A210
The L3 detector at the CERN electron-positron collider had a muon spectrometer which was employed during the last years of LEP operation for cosmic ray studies. The results of this program include a precise muon spectrum and charge ratio between 20 GeV and 3 TeV, a limit on TeV primary antiprotons from a study of the Moon’s shadow, the (possible) observation of a are signal from a fixed position in the northern hemisphere through muons, a solar anisotropy of 200 GeV protons, and other results. Negative limits on muons associated with known H.E. gamma sources or gamma bursts, the search for anomalous H.E. interaction or decay events such as reported from the Kolar Gold Fields, and a search for muons correlated with a solar are are also noted. 相似文献
978.
Tom Kennedy 《Journal of statistical physics》2008,131(5):803-819
We simulate several models of random curves in the half plane and numerically compute the stochastic driving processes that
produce the curves through the Loewner equation. Our models include models whose scaling limit is the Schramm-Loewner evolution
(SLE) and models for which it is not. We study several tests of whether the driving process is Brownian motion, as it is for
SLE. We find that testing only the normality of the process at a fixed time is not effective at determining if the random
curves are an SLE. Tests that involve the independence of the increments of Brownian motion are much more effective. We also
study the zipper algorithm for numerically computing the driving function of a simple curve. We give an implementation of
this algorithm which runs in a time O(N
1.35) rather than the usual O(N
2), where N is the number of points on the curve. 相似文献
979.
Aditya M. Vora 《Central European Journal of Physics》2008,6(2):238-252
Ashcroft’s empty core (EMC) model potential is used to study the superconducting state parameters (SSPs) viz. electron-phonon
coupling strength λ, Coulomb pseudopotential μ*, transition temperature T
C
, isotope effect exponent αand effective interaction strength N
O
V of some binary metallic glasses based on the superconducting (S), conditional superconducting (S’) and non-superconducting
(NS) elements of the periodic table. Five local field correction functions proposed by Hartree (H), Taylor (T), Ichimaru-Utsumi
(IU), Farid et al. (F) and Sarkar et al. (S) are used for the first time with EMC potential in the present investigation to study the screening influence on the aforesaid
properties. The T
C
obtained from the H-local field correction function are in excellent agreement with available theoretical or experimental
data. In the present computation, the use of the pseudo-alloy-atom model (PAA) was proposed and found successful. Present
work results are in qualitative agreement with such earlier reported experimental values which confirm the superconducting
phase in all metallic glasses. A strong dependency of the SSPs of the metallic glasses on the valence ‘Z’ is identified.
相似文献
980.
We present the number of dimer coverings N
d
(n) on the Sierpinski gasket SG
d
(n) at stage n with dimension d equal to two, three, four or five. When the number of vertices, denoted as v(n), of the Sierpinski gasket is an even number, N
d
(n) is the number of close-packed dimers. When the number of vertices is an odd number, no close-packed configurations are possible
and we allow one of the outmost vertices uncovered. The entropy of absorption of diatomic molecules per site, defined as
, is calculated to be ln (2)/3 exactly for SG
2. The numbers of dimers on the generalized Sierpinski gasket SG
d,b
(n) with d=2 and b=3,4,5 are also obtained exactly with entropies equal to ln (6)/7, ln (28)/12, ln (200)/18, respectively. The number of dimer
coverings for SG
3 is given by an exact product expression, such that its entropy is given by an exact summation expression. The upper and lower
bounds for the entropy are derived in terms of the results at a certain stage for SG
d
(n) with d=3,4,5. As the difference between these bounds converges quickly to zero as the calculated stage increases, the numerical
value of
with d=3,4,5 can be evaluated with more than a hundred significant figures accurate.
This paper is written during the Lung-Chi Chen visit to PIMS, University of British Columbia. The author thanks the institute
for the hospitality. 相似文献