全文获取类型
收费全文 | 362557篇 |
免费 | 36894篇 |
国内免费 | 283篇 |
出版年
2018年 | 3421篇 |
2016年 | 4606篇 |
2015年 | 5859篇 |
2014年 | 6756篇 |
2013年 | 10101篇 |
2012年 | 10810篇 |
2011年 | 11239篇 |
2010年 | 7694篇 |
2009年 | 6942篇 |
2008年 | 10095篇 |
2007年 | 10162篇 |
2006年 | 9674篇 |
2005年 | 9218篇 |
2004年 | 9110篇 |
2003年 | 8830篇 |
2002年 | 8480篇 |
2001年 | 15534篇 |
2000年 | 15358篇 |
1999年 | 12070篇 |
1998年 | 4306篇 |
1997年 | 4514篇 |
1996年 | 4297篇 |
1995年 | 3850篇 |
1994年 | 3799篇 |
1993年 | 3831篇 |
1992年 | 9984篇 |
1991年 | 9991篇 |
1990年 | 9695篇 |
1989年 | 9414篇 |
1988年 | 8696篇 |
1987年 | 8353篇 |
1986年 | 7629篇 |
1985年 | 7833篇 |
1984年 | 6467篇 |
1983年 | 5489篇 |
1982年 | 4217篇 |
1981年 | 3939篇 |
1980年 | 3640篇 |
1979年 | 6255篇 |
1978年 | 4830篇 |
1977年 | 4629篇 |
1976年 | 4309篇 |
1975年 | 4837篇 |
1974年 | 5307篇 |
1973年 | 5283篇 |
1972年 | 4741篇 |
1971年 | 4376篇 |
1970年 | 3901篇 |
1969年 | 3857篇 |
1968年 | 3521篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
961.
The paper presents the results of theoretical and experimental studies of the radiative properties of plasmas produced by
heating and compression of various materials to high energy densities. The specific features of the theoretical plasma model
known as the ion model, which is used to calculate the radiative characteristics of plasmas of complex chemical composition,
are discussed. The theoretical approach based on this model is applied to the plasma produced during the explosion of the
X-pinch wires. The theoretical estimate of the radiation efficiency is compared with the experimental data on the total energy
yield from an X-pinch made of two different wires (NiCr and Alloy 188). The radiative characteristics of (C12 H16 O8) and
(C8 H12 O6) plasmas are calculated for the temperature diagnostics of plasmas produced from porous targets employed in inertial
confinement fusion experiments with the use of laser radiation and heavy-ion beams. 相似文献
962.
Pedal progression of the slug Limax maximus was studied to obtain relations between wave velocity on the sole of the foot, wave frequency, the advance due to a single wave, and the velocity of vertically upward creeping. Each of the first three quantities is directly proportional to the simultaneous velocity of progression. Under comparable conditions, that is when work is done at a constant rate, the frequency of pedal waves is influenced by the temperature according to the equation of Arrhenius, with µ = 10,700 (Q
10 for 11° to 21° = 2.1). The velocity of a single wave must have very nearly the same "temperature characteristic," which is found also in another case of nerve net transmission (in Renilla). 相似文献
963.
964.
965.
Identification of the protein HC receptor 总被引:2,自引:0,他引:2
In the present study, we demonstrate for the first time the presence of a specific receptor for protein HC on the surface of human cells using the human histiocytic lymphoma cell line U937. Cells treated for 4 days with the maturation inducer phorbol 12-myristate 13-acetate, were found to increase both the number of cells binding protein HC (76% higher than for untreated cells) and the expression of protein HC receptors. Protein HC bound to these cells in a specific and saturable manner. Scatchard analysis at 4 degrees C, using radioiodinated protein HC, indicated a single class of low-affinity receptor (Ka = 2-5 x 10(7) M-1) and 20,000-30,000 receptors per cell. Monoclonal antibodies against protein HC abrogated specific binding of this protein to U937. In contrast, monoclonal antibodies that did not react with protein HC (anti-LFA-1 alpha, anti-MO1 alpha) were without effect on the binding reaction. 相似文献
966.
Fertilizer application to rice-fields in the river-deltas in the Mediterranean area is a potential menace for wildlife protection, through eutrophication.Fertilizer use shows a trend of increasing rates of N application. A rate for N of 200 kg ha–1 has become normal and a rate of 400 kg ha–1 has already been recorded.Denitrification causes large losses of N with the result that more fertilizer is applied. This is especially true for the Camargue (S-France), where N is applied long before the rice (Aryza sativa) can take it up.Therefore we have tried to develop techniques which need the application of smaller amounts of N which are used more efficiently. In order to do this we tried to establish a N budget for rice-fields.Experiments were therefore set up in the field (plots of 550 m2) and in pots (2–3 l). Our results suggest that a late application of N (e.g. when the rice shows signs of N-deficiency by becoming yellowish), but at lower concentrations (70 kg ha–1) can produce the same ultimate yield. The introduction of carp without any further input of N produced the same final yield.The N budget shows that 15±1.5 g m–2 of N is needed for a normal crop. N losses due to denitrification may be as high as 12.2–13.6 g m–2 of N. The input by irrigation water may provide up to about 20% of the input; N fixation is negligible. We estimate that 25–50% of the N missing in the budget comes from minderalization of the organic N pool in the soil. Denitrification may render part of this pool bio-available by oxidation. In sum, this work has revealed some surprising effects with potentially important consequences for farming practice and, in consequence, for conservation. 相似文献
967.
V. Cencora F. Challoner S. Gooch A. Livingstone D. Widgery 《BMJ (Clinical research ed.)》1988,297(6646):481-483
968.
S Papa M Vitale G Mazzotti R Rizzoli M Falconi A Bartoletti F A Manzoli 《Histochemistry》1988,89(3):241-245
A number of techniques are currently employed for the fractionation of heterogeneous cell populations or for the separation of cells in different phases of their cycle. With the development of osmotically inert colloidal silica particles media, density gradient centrifugation became an established method for the separation and purification of cells and subcellular particles. We have applied this technique to the separation of cycling from resting Friend erythroleukemia cells, to obtain purified populations for further biological assays. The flow cytometric analysis of DNA content of the different fractions obtained by the gradient and stained with Propidium Iodide (PI), showed the S compartment highly concentrated in the 1.073/77 g/ml interface, while the upper levels of the gradient were highly enriched of cells in G1 phase. Moreover, the dual parameter analysis of DNA content by means of Bromodeoxyuridine (BrdUrd) incorporation and PI staining, showed that part of the cells in the 1.067/73 fraction represented the early S phase even if their DNA level, measured on the basis of PI fluorescence was within the diploid cell cluster. This method seems to be suitable to obtain pure cell fractions even when dealing with numerically large populations. 相似文献
969.
970.