全文获取类型
收费全文 | 9428篇 |
免费 | 379篇 |
国内免费 | 37篇 |
专业分类
化学 | 7329篇 |
晶体学 | 74篇 |
力学 | 147篇 |
数学 | 1096篇 |
物理学 | 1198篇 |
出版年
2023年 | 100篇 |
2022年 | 88篇 |
2021年 | 451篇 |
2020年 | 278篇 |
2019年 | 273篇 |
2018年 | 234篇 |
2017年 | 204篇 |
2016年 | 368篇 |
2015年 | 287篇 |
2014年 | 391篇 |
2013年 | 617篇 |
2012年 | 680篇 |
2011年 | 737篇 |
2010年 | 497篇 |
2009年 | 385篇 |
2008年 | 596篇 |
2007年 | 573篇 |
2006年 | 513篇 |
2005年 | 409篇 |
2004年 | 336篇 |
2003年 | 255篇 |
2002年 | 219篇 |
2001年 | 122篇 |
2000年 | 88篇 |
1999年 | 77篇 |
1998年 | 71篇 |
1997年 | 56篇 |
1996年 | 66篇 |
1995年 | 52篇 |
1994年 | 51篇 |
1993年 | 49篇 |
1992年 | 52篇 |
1991年 | 46篇 |
1990年 | 36篇 |
1989年 | 45篇 |
1988年 | 32篇 |
1987年 | 38篇 |
1986年 | 34篇 |
1985年 | 60篇 |
1984年 | 40篇 |
1983年 | 28篇 |
1982年 | 44篇 |
1981年 | 29篇 |
1980年 | 31篇 |
1979年 | 19篇 |
1978年 | 14篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1974年 | 11篇 |
1973年 | 10篇 |
排序方式: 共有9844条查询结果,搜索用时 15 毫秒
51.
Jacob S. Ishay Anna Sverdlov Vitaly Pertsis Yulla Gavrilov David Steinberg 《Photochemistry and photobiology》2004,80(1):115-118
In the cuticle of live social hornets, such as Vespa orientalis (Hymenoptera, Vespinae), endogenous electric effects are encountered, i.e. voltages of 100–200 mV under illumination and currents amounting to several microamperes on its subjection to darkness—clearly a process of charging and discharging. Of the various wavelengths of sunlight, UV was found to be the most contributory to the active cuticular voltage generation. Throughout the warm season of the yearthe–the active period in colonies of social hornets and wasps—colony members exit from the dark nest during the daytime and fly to the field under the hot sun for various foraging purposes, ultimately returning to the nest. Thus, each hornet, be it queen, worker or drone, probably undergoes daily cyclical process of electric charge and discharge in the exterior part of their integument, cuticle, which lasts up to 30–40 min. Such photoelectric phenomenon was detected in both live, ether‐anaesthetized hornets and dead hornets, albeit in the latter the electric values recorded were lower. The present study addresses the possible impact of the phenomenon on vespan daily life and also compares it with a parallel occurrence in electric fish. 相似文献
52.
53.
The field of medicinal inorganic chemistry is rapidly advancing. In particular organometallic complexes have much potential as therapeutic and diagnostic agents. The carbon‐bound and other ligands allow the thermodynamic and kinetic reactivity of the metal ion to be controlled and also provide a scaffold for functionalization. The establishment of structure–activity relationships and elucidation of the speciation of complexes under conditions relevant to drug testing and formulation are crucial for the further development of promising medicinal applications of organometallic complexes. Specific examples involving the design of ruthenium and osmium arene complexes as anticancer agents are discussed. 相似文献
54.
Pal Jen Wei 《Journal of Non》2008,354(33):3911-3918
Through the arrangement of the applied load, experimental nanoindentation results of polymethylmethacrylate (PMMA) and polyurethane (PU) employed to establish a mechanical model. The proposed model consists of irreversible delayed plastic (viscoplastic) deformation, irreversible viscous deformation, and reversible delayed elastic (viscoelastic) deformations. The phase lag exhibited between the responding depth and the oscillating load is found to be linear proportional to frequency in the range of 1-50 Hz. The residual cavity profile of the PMMA scanned by an atomic force microscope gives a validity of accommodation assumption applied in the present model. The effects of overshooting, which occurred in the dwelling process, are also discussed. 相似文献
55.
The vertical migration of 85Sr, 137Cs and 131I in some arable and undisturbed single-contaminated soils was studied by gamma-spectrometry measurements under lysimetric laboratory conditions during irrigation of the soil profiles with wet atmospheric precipitation for about one year, except 131I. A new simple exponential compartment (box) model was derived, which makes it possible to calculate the migration rate constants and migration rates in the individual soil layers (vertical sections) as well as the total vertical migration rate constants and total vertical migration rates of radionuclides in the bulk soil horizon. The relaxation times of radionuclides in respective soil horizons can also be evaluated. 相似文献
56.
57.
R. U. Khan P. Chakrabarti B. B. Pal 《Applied Physics A: Materials Science & Processing》1987,42(4):303-309
Large signal characterisation of double heterostructure DDR Impatt diode has been carried out in the millimeter-wave range considering the MITATT mode of operation. The structure of the device is p+-p2-p1-n1-n2-n+ where impact ionisation and tunneling takes place in the p1-n1 region. In this study we have considered two well-known heterostructures, e.g., InP/GaInAs/InP and InP/InGaAsP/InP and one nonconventional structure GaAs/InP/GaAs. The theoretical results of the performances of these devices as regards of output power, efficiency, and negative conductance revealed that the structures are quite promising as the source of power in the millimeter-wave range. The analysis may be used for other mm wave DDR heterostructure Impatts. 相似文献
58.
Anna Valette-Stasica 《Topology and its Applications》2007,154(2):443-448
Using algebraically constructible functions we give a generically effective method to detect asymptotic values of polynomial mappings with finite fibers defined on the real plane. By asymptotic variety we mean the set of points at which the polynomial mapping fails to be proper. 相似文献
59.
We couple a morphological study of an immiscible binary AB mixture with a micromechanical simulation to determine how the spatial distribution of the A and B domains and the interfacial region (interphase) affects the mechanical behavior of the blend. The morphological studies are conducted through a three-dimensional Cahn-Hilliard (CH) simulation. Through the CH calculations, we obtain the size and structure of the domains for different blend compositions. The output of the CH model serves as the input to the Lattice Spring Model (LSM), which consists of a three-dimensional network of springs. In particular, the location of the different phases is mapped onto the LSM lattice and the appropriate force constants are assigned to the LSM sites. A stress is applied to the LSM lattice and we calculate the elastic response of the material. We find that the local stress and strain fields are highly dependent on the morphology of the system. By integrating the morphological and mechanical models, we can isolate how modifications in the composition of the mixture affect the macroscopic behavior. Thus, we can establish how choices made in the components affect the ultimate performance of the material. 相似文献
60.
In this paper we face the problem of stowing a containership, referred to as the Master Bay Plan Problem (MBPP); this problem
is difficult to solve due to its combinatorial nature and the constraints related to both the ship and the containers. We
present a decomposition approach that allows us to assign a priori the bays of a containership to the set of containers to
be loaded according to their final destination, such that different portions of the ship are independently considered for
the stowage. Then, we find the optimal solution of each subset of bays by using a 0/1 Linear Programming model. Finally, we
check the global ship stability of the overall stowage plan and look for its feasibility by using an exchange algorithm which
is based on local search techniques. The validation of the proposed approach is performed with some real life test cases.
This work has been developed within the research area: “The harbour as a logistic node” of the Italian Centre of Excellence
on Integrated Logistics (CIELI) of the University of Genoa, Italy 相似文献