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981.
J. M. Schultz 《Journal of Polymer Science.Polymer Physics》1992,30(7):785-786
982.
阮颖彬 《应用泛函分析学报》2002,4(2):97-103
讨论了Banach空间X上两个算子T,S拟相似时,近似点谱σα(T)的每一个连通分支与σα(S)以及σs(S)的相交关系,证明了σα(T)的每一个连通分支与σs(S)的交非空,并且给出了σα(T)的连通分支与σα(S)交非空的充要条件。 相似文献
983.
For twice smooth functions, the symmetry of the matrix of second partial derivatives is automatic and can be seen as the symmetry of the Jacobian matrix of the gradient mapping. For nonsmooth functions, possibly even extended-real-valued, the gradient mapping can be replaced by a subgradient mapping, and generalized second derivative objects can then be introduced through graphical differentiation of this mapping, but the question of what analog of symmetry might persist has remained open. An answer is provided here in terms of a derivative-coderivative inclusion. 相似文献
984.
由Q-开关Nd:YAG激光器产生的1.06μm、10ns的脉冲激光辐射大气中的铝靶所产生的等离子体发射光谱的研究结果。当作用在铝靶表面的功率密度在1.0×10 ̄9W/cm ̄2-1.4×10 ̄(10)W/cm ̄2范围时,测定了等离子体在200至880nm波长范围内的空间、时间分辨发射光谱。实验发现,等离子体中N ̄+离子的辐射谱线与连续辐射同时出现并一起消失,随激光强度的增加N ̄+离子密度以指数关系增加,在激光源方向N ̄+离子的运动速度为零。从靶表面逸出的热电子与氮原子碰撞及随后发生的级联电离过程是产生N ̄+离子和空气等离子体的原因。 相似文献
985.
M. Costa G. P. Chiusoli R. Gaetti B. Gabriele G. Salerno 《Russian Chemical Bulletin》1998,47(5):936-940
New rhodium-catalyzed amination reactions of arylacetylenes and cyclohexen-1-ylacetylene in the presence of strong bases with
the use of carbon dioxide as an auxiliary are described. Secondary amines attack the terminal carbon atom of the triple bond
followed by protonation of the adjacent carbon atom. Alternatively, the reaction can proceed further with the addition of
the second alkyne molecule. The conditions for the selective synthesis of enamines (up to 87% yield) or α-substituted propynylamines
(up to 86% yield) are reported.
Dipartimento di Chimica Organica e Industriale dell'Università, Viale delle Scienze, I-43100 Parma, Italia.
Dipartimento di Chimica, Università della Calabria, Arcavacata di Rende, I-80036 Cosenza, Italia.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 966–970, May, 1998. 相似文献
986.
E. Amaldi E. Coccia C. Cosmelli Y. Ogawa G. Pizzella P. Rapagnani F. Ricci P. Bonifazi M. G. Castellano G. Vannaroni F. Bronzini P. Carelli V. Foglietti G. Cavallari R. Habel I. Modena G. V. Pallottino 《Il Nuovo Cimento C》1984,7(3):338-354
Summary We report on the cooling at liquid-helium temperature of our 2270 kg 5056 Al bar at CERN. The liquid-helium container had
been filled up to 1500 liters ensuring to keep the antenna cold for more than one month. The antenna is equipped with a resonant
capacitive transducer operating at constant electrical charge with a FET low-noise amplifier. The transducer is tuned to the
antenna within less than I Hz and the two normal-mode frequencies are ν−=908.160 Hz and ν+=924.234 Hz with an applied electrical field in the transducer of 106 V/m. The corresponding overall merit factors areQ
−=5.20·106 andQ
+=7.25·106. The transducer has been tested up to an electrical field of 6·106 V/m: in this condition we have βQ≈104. The antenna has been in operation for several weeks giving, for the Brownian noise, values in agreement with the calculated
values. We report also on the results of tests performed on a DC SQUID, whose input was connected to a commercial capacitor
via a transformer with turn ratio of 1000.
Supported in part by Japan Society for the Promotion of Science. 相似文献
987.
In flat spacetime, the fourth space coordinate in special relativity (SR) is equivalent to the coordinate time tE. We will show, however, that this definition of physical time is not unique. Another natural choice of coordinate time, tA, with absolute synchronization is allowed. Spacetime would exhibit dual properties, namely relativistic and absolute. In an arbitrary inertial frame, the relationship of the above two kinds of coordinate time corresponds to a resynchronization, and the Lorentz transformations can be written in an alternative form, which is called the generalized Galilean transformation (GGT). Although the absolute property is still hidden in nearly all types of experiments, the advantages of the above approach are as follows: (1) It will give us a deeper understanding of SR, including the basis of length contraction, time dilation and the interaction between moving objects and the physical vacuum. (2) It will provide a wider research domain than SR; for example, superluminal motion is predicted and has obtained growing experimental support. 相似文献
988.
用低杂波的可的性条件,参量不稳定条件和功率耦合谱分析了低杂波电流驱动。由于波的可近性条件限制耦合谱中平行相速度较大的波进入等离子体中心,参量不稳定性使平行相速度较低的波与离子相互作用,随着等离子体密度的增中,这些作用越来越明显,最终导致低杂波不能在中心与电子相互作用,驱动电流消失,这就是所谓密度极限。在本文建立的模型基础上的计算结果与实验结果符合较好。 相似文献
989.
The generalized assignment problem can be viewed as the following problem of scheduling parallel machines with costs. Each job is to be processed by exactly one machine; processing jobj on machinei requires timep
ij
and incurs a cost ofc
ij
; each machinei is available forT
i
time units, and the objective is to minimize the total cost incurred. Our main result is as follows. There is a polynomial-time algorithm that, given a valueC, either proves that no feasible schedule of costC exists, or else finds a schedule of cost at mostC where each machinei is used for at most 2T
i
time units.We also extend this result to a variant of the problem where, instead of a fixed processing timep
ij
, there is a range of possible processing times for each machine—job pair, and the cost linearly increases as the processing time decreases. We show that these results imply a polynomial-time 2-approximation algorithm to minimize a weighted sum of the cost and the makespan, i.e., the maximum job completion time. We also consider the objective of minimizing the mean job completion time. We show that there is a polynomial-time algorithm that, given valuesM andT, either proves that no schedule of mean job completion timeM and makespanT exists, or else finds a schedule of mean job completion time at mostM and makespan at most 2T.
Research partially supported by an NSF PYI award CCR-89-96272 with matching support from UPS, and Sun Microsystems, and by the National Science Foundation, the Air Force Office of Scientific Research, and the Office of Naval Research, through NSF grant DMS-8920550.Research supported in part by a Packard Fellowship, a Sloan Fellowship, an NSF PYI award, and by the National Science Foundation, the Air Force Office of Scientific Research, and the Office of Naval Research, through NSF grant DMS-8920550. 相似文献
990.
Ulf Ryde 《Journal of computer-aided molecular design》1996,10(2):153-164
Summary The coordination number of the catalytic zinc ion in alcohol dehydrogenase has been studied by integrated ab initio quantum-chemical and molecular mechanics geometry optimisations involving the whole enzyme. A four-coordinate active-site zinc ion is 100–200 kJ/mol more stable than a five-coordinate one, depending on the ligands. The only stable binding site for a fifth ligand at the zinc ion is opposite to the normal substrate site, in a small cavity buried behind the zinc ion. The zinc coordination sphere has to be strongly distorted to accommodate a ligand in this site, and the ligand makes awkward contacts with surrounding atoms. Thus, the results do not support proposals attributing an important role to five-coordinate zinc complexes in the catalytic mechanism of alcohol dehydrogenase. The present approach makes it possible also to quantify the strain induced by the enzyme onto the zinc ion and its ligands; it amounts to 42–87 kJ/mol for four-coordinate active-site zinc ion complexes and 131–172 kJ/mol for five-coordinate ones. The four-coordinate structure with a water molecule bound to the zinc ion is about 20 kJ/mol less strained than the corresponding structure with a hydroxide ion, indicating that the enzyme does not speed up the reaction by forcing the zinc coordination sphere into a structure similar to the reaction intermediates. 相似文献