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991.
We present the phase diagrams and the properties of newly synthesised double-chain cationic N-alkyl-N-alkyl′-N,N-dimethylammonium bromide surfactants [C
x
C
y
DMABr (x = 12, 14 and 16; y = 10, 11, 12, 14 and 16)]. All the systems studied form liquid-crystalline lamellar phases but with different morphologies:
unilamellar vesicles at low surfactant concentrations, multilamellar vesicles and tubular aggregates for surfactant concentrations
between 2 and 10 wt% and at even higher concentrations planar bilayers of surfactant molecules in the classical Lα phase. The phase diagrams were determined with macroscopic and microscopic methods (polarisation microscopy, freeze-fracture
transmission electron microscopy, scanning electron microscopy and differential interference contrast microscopy). The properties
of the surfactant solutions were determined with differential scanning calorimetry measurements for Krafft point determination
and small-angle neutron scattering measurements for interlamellar spacing and bilayer thickness. Finally, conductivity and
viscosity measurements for phase characterisation were carried out.
Received: 7 April 1999 Accepted in revised form: 30 April 1999 相似文献
992.
C. Herberg M. Ostrick H.G. Andresen J.R.M. Annand K. Aulenbacher J. Becker P. Drescher D. Eyl A. Frey P. Grabmayr S.J. Hall P. Hartmann T. Hehl W. Heil J. Hoffmann D. Ireland J.D. Kellie F. Klein K. Livingston Ch. Nachtigall A. Natter E.W. Otten R.O. Owens E. Reichert D. Rohe H. Schmieden R. Sprengard M. Steigerwald K.-H. Steffens Th. Walcher R. Watson 《The European Physical Journal A - Hadrons and Nuclei》1999,5(2):131-135
The electric form factor of the neutron G
E,n has been determined at the Mainz Microtron MAMI at the low momentum transfer Q
2= 0.15 (GeV/c)2 in a measurement of the recoil polarisation ratio P
x/Pz in the quasifree reaction D(e,e′n)p. At this Q
2 the influence of the nuclear binding is strong. A purely kinematical model is used to get some insight into the effect of
the initial Fermi momentum distribution of the neutron. The influence of the final state interaction is determined quantitatively
by a model of Arenh?vel et al.. After the corresponding corrections a value of G
E,n(0.15 (GeV/c)2) = 0.0481±0.0065stat±0.0053syst is obtained.
Received: 12 April 1999 相似文献
993.
Rainer Pttgen Rolf‐Dieter Hoffmann Jan Renger Ute Ch. Rodewald Manfred H. Mller 《无机化学与普通化学杂志》2000,626(11):2257-2263
New intermetallic rare earth compounds REAuMg (RE = Y, La–Nd, Sm, Eu, Gd–Yb) were synthesized by reaction of the elements in sealed tantalum tubes in a high‐frequency furnace. The compounds were investigated by X‐ray diffraction both on powders and single crystals. Some structures were refined on the basis of single crystal data. The compounds with Y, La–Nd, Sm, and Gd–Tm adopt the ZrNiAl type structure with space group P62m: a = 770.8(2), c = 419.5(1) pm, wR2 = 0.0269, 261 F2 values for PrAuMg, a = 750.9(2), c = 407.7(1) pm, wR2 = 0.0561, 649 F2 values for HoAuMg with 15 variables for each refinement. Geometrical motifs in HoAuMg are two types of gold centered trigonal prisms: [Au1Mg3Ho6] and [Au2Mg6Ho3]. The gold and magnesium atoms form a three‐dimensional [AuMg] polyanion in which the holmium atoms fill distorted hexagonal channels. The magnesium positions show a small degree of magnesium/gold mixing resulting in the refined compositions PrAu1.012(2)Mg0.988(2) and HoAu1.026(3)Mg0.974(3). EuAuMg and YbAuMg contain divalent europium and ytterbium, respectively. Both compounds crystallize with the TiNiSi type structure, space group Pnma: a = 760.6(3), b = 448.8(2), c = 875.8(2) pm, wR2 = 0.0491, 702 F2 values, 22 variables for EuAuMg, and a = 738.4(1), b = 436.2(1), c = 864.6(2) pm, wR2 = 0.0442, 451 F2 values, and 20 variables for YbAuMg. The europium position shows a small degree of europium/magnesium mixing, and the magnesium site a slight magnesium/gold mixing leading to the refined composition Eu0.962(3)Au1.012(3)Mg1.026(3). No mixed occupancies were found in YbAuMg where all sites are fully occupied. In these structures the europium(ytterbium) and magnesium atoms form zig‐zag chains of egde‐sharing trigonal prisms which are centered by the gold atoms. As is typical for TiNiSi type compounds, also in EuAuMg and YbAuMg a three‐dimensional [AuMg] polyanion occurs in which the europium(ytterbium) atoms are embedded. The degree of distortion of the two polyanions, however, is different. 相似文献
994.
995.
996.
997.
Arne Warth Esther Herpel Sabine Krysa Hans Hoffmann Philipp A. Schnabel Peter Schirmacher Gunhild Mechtersheimer Hendrik Bl?ker 《Experimental & molecular medicine》2009,41(5):349-353
Pulmonary carcinoids are infrequent neoplasms of the lung that normally display a less aggressive biological behavior compared to small cell and non-small cell lung cancers. Approximately 15-25% of carcinoids, in particular atypical carcinoids, show lymph node metastasis and have a worse prognosis than their non-metastasized counterparts. To date, there is no morphological or molecular marker that may help to differentiate between carcinoids that metastasize and carcinoids of identical differentiation that show only local tumor growth. In this study, we analyzed 7 metastasized and 10 non-metastasized pulmonary carcinoids for chromosomal and microsatellite instability in order to determine whether microsatellite instability or chromosomal imbalances are associated with metastasis. Due to the rare occurrence of metastasized carcinoids we compared our results of chromosomal instability with the hitherto published comparative genomic hybridization (CGH) profiles of pulmonary carcinoids, for which information about the absence or presence of metastasis was available. While microsatellite instability was not detected we found chromosomal instability as a common event in pulmonary carcinoids with an increase of frequency and extent of chromosomal alterations in atypical and metastasized carcinoids. These findings are in accordance with the collected and herein compiled data of previous studies and indicate increasing numbers of chromosomal imbalances to play a role in the sequential process of tumor development and metastasis. 相似文献
998.
We look at the computational complexity of 2-dimensional geometric optimization problems on a finite point set with respect to the number of inner points (that is, points in the interior of the convex hull). As a case study, we consider the minimum weight triangulation problem. Finding a minimum weight triangulation for a set of n points in the plane is not known to be NP-hard nor solvable in polynomial time, but when the points are in convex position, the problem can be solved in O(n3) time by dynamic programming. We extend the dynamic programming approach to the general problem and describe an exact algorithm which runs in O(6kn5logn) time where n is the total number of input points and k is the number of inner points. If k is taken as a parameter, this is a fixed-parameter algorithm. It also shows that the problem can be solved in polynomial time if k=O(logn). In fact, the algorithm works not only for convex polygons, but also for simple polygons with k inner points. 相似文献
999.
1000.
Zhiming Chen K.-H. Hoffmann Jin Liang 《Mathematical Methods in the Applied Sciences》1993,16(12):855-875
In this paper, we study a non-stationary superconductivity model derived from Ginzburg–Landau macroscopic theory. By using gauge invariance and studying a linear problem with curl boundary conditions, we obtain the existence of solutions. The solution is unique in the sense of gauge equivalence. 相似文献