全文获取类型
收费全文 | 1135篇 |
免费 | 42篇 |
国内免费 | 20篇 |
专业分类
化学 | 611篇 |
晶体学 | 2篇 |
力学 | 59篇 |
数学 | 340篇 |
物理学 | 185篇 |
出版年
2023年 | 12篇 |
2022年 | 39篇 |
2021年 | 44篇 |
2020年 | 50篇 |
2019年 | 46篇 |
2018年 | 49篇 |
2017年 | 39篇 |
2016年 | 57篇 |
2015年 | 26篇 |
2014年 | 48篇 |
2013年 | 92篇 |
2012年 | 64篇 |
2011年 | 60篇 |
2010年 | 46篇 |
2009年 | 35篇 |
2008年 | 56篇 |
2007年 | 52篇 |
2006年 | 28篇 |
2005年 | 29篇 |
2004年 | 29篇 |
2003年 | 20篇 |
2002年 | 22篇 |
2001年 | 6篇 |
2000年 | 12篇 |
1999年 | 12篇 |
1998年 | 11篇 |
1997年 | 13篇 |
1996年 | 10篇 |
1995年 | 14篇 |
1994年 | 10篇 |
1993年 | 8篇 |
1992年 | 6篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1987年 | 7篇 |
1985年 | 14篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 8篇 |
1977年 | 11篇 |
1976年 | 7篇 |
1975年 | 9篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有1197条查询结果,搜索用时 15 毫秒
271.
272.
Vo Dac Bang Tran Dai Nghiep Tran Duc Thiep Sh. Gerbish Phan Thu Huong Pham Thi Nam 《Journal of Radioanalytical and Nuclear Chemistry》1984,86(5):291-302
The combination of photon and neutron activation provides an effective method of analysis of rare earths and other elements. A mixed -neutron field is obtained with electron-to-gamma /e/ and gamma-to-neutron /n/ converters combined with a lucite moderator. The samples are activated simultaneously. The sensitivities of this method have been compared with neutron activation in a graphite moderator cube using the same microtron. The advantages and shortcomings of the method are discussed.Dedicated to Prof. V.D. Nefedov on the occasion of his 70th birthday 相似文献
273.
Some symptoms of excessive seepage of water were observed at the earthfill dam of the 400 MW Tri An hydropower plant in South Viet Nam. To provide experimental information for assessing the situation, isotope tracer experiments were performed using 24 existing piezometric boreholes encompassing a 1100 m long middle section of the dam. Filtration velocities measured were in the ranges (0.2–30) cm d–1 in the dam body and (0.5–75) cm d–1 in subsurface strata. No abnormally permeable horizons were detected. Permeability coefficients were calculated and compared with that obtained in pre-project hydrogeological surveys and by field tests during dam construction. Tracer experiments yielded permeability of the same range for the subsurface aquifer but from one to two orders of magnitude higher for the dam body. Such a dramatic change of permeability of the dam body me dia is interpreted as a result of interaction with seeping water after reservoir impoundment. A transient erosion process took place during several years. The losses of water by seepage through the dam body and infiltration to underground water were estimated as 1100 m3 d–1 and 15,000 m3 d–1 respectively, less than 1/2000 of the quantity of water consumed for power generation. A multi-well interconnection experiment was performed to determine the velocity and direction of subsurface flows. 相似文献
274.
Pham Loi Vu 《Acta Appl Math》2010,109(3):765-787
We derive the continual system of nonlinear interaction waves from the compatibility of the transport equation on the whole line and the equation governing the time-evolution of the eigenfunctions of the transport operator. The transport equation represents the continual generalization from the n-component system of first-order ordinary differential equations. The continual system describes a nonlinear interaction of waves. We prove that the continual system can be integrated by the inverse scattering method. The method is based on applying the results of the inverse scattering problem for the transport equation to finding the solution of the Cauchy initial-value problem for the continual system. Indeed, the transition operator for the scattering problem admits right and left Volterra factorizations. The intermediate operator for this problem determines the one-to-one correspondence between the preimages of a solution of the transport equation. This operator is related to the transition operator and admits not only right and left Volterra factorizations but also the analytic factorization. By virtue of this fact the potential in the transport equation is uniquely reconstructed in terms of the solutions of the fundamental equations in inverse problem.We introduce the generalized Lax equation. This enables us to derive the time-evolution of the transition operator. Then, the time-dependent intermediate operator is constructed. The solution of the considered Cauchy problem is expressed in terms of solutions of the fundamental equations in inverse problem. This solution is found uniquely from the given initial condition. 相似文献
275.
Dinh Tuan Pham Joachim Möcks Lothar Sroka 《Annals of the Institute of Statistical Mathematics》1989,41(3):415-427
The paper provides sufficient conditions for the asymptotic normality of statistics of the form a
ijbRiRj, wherea
ijandb
ijare real numbers andR
iis a random permutation. 相似文献
276.
A.Q. Pham N. Merrien A. Maignan F. Studer C. Michel B. Raveau 《Physica C: Superconductivity and its Applications》1993,210(3-4):350-358
The metal-insulator transition in the solid solution Bi2Sr2Ca1−xYxCu2O8+δ (0≤x≤1) has been investigated by TGA (oxygen content) and by X-ray absorption spectroscopy (Bi and Cu valence states). Resistivity and AC magnetic susceptibility measurements have shown that the superconducting properties and the metallic behavior vanish for x>0.55. The oxygen content δ is larger than x/2 for x≤0.3 and smaller than x/2 for x≥0.6. For x=0, the Cu K edge shows a shift towards high energy with respect to the Cu(II) oxide La2CuO4; this shift decreases with increasing x in agreement with the decrease of the doping hole density and the variations of the physical properties. For 0≤x≤0.3, the Bi L3 edge shows a shift of 1 eV towards low energy with respect to the Bi(III) oxide Bi2O3 in agreement with the charge transfer between [CuO2]∞ and [BiO]∞ planes. This shift also decreases with increasing x, but is still present for the x=0.6 composition for which δ is smaller than x/2. A model of the metal-insulator transition in this series is proposed based on the fact that the intercalation of excess oxygen raises the bottom of the Bi-O band with respect to the Fermi level and decreases the contribution of the Bi-O electron pocket to the hole density. 相似文献
277.
T H Pham R Hornung M W Berns Y Tadir B J Tromberg 《Photochemistry and photobiology》2001,73(6):669-677
Benzoporphyrin-derivative (BPD)-monoacid-ring A photodynamic therapy (PDT) was performed on subcutaneous tumor implants in a rat ovarian cancer model. In order to assess PDT efficacy the tumor and normal tissue optical properties were measured noninvasively prior to and during PDT using frequency-domain photon migration (FDPM). FDPM data were used to quantify tissue absorption and reduced scattering properties (given by the parameters mu a and mu's, respectively) at four near-infrared (NIR) wavelengths (674, 811, 849 and 956 nm). Tissue physiologic properties, including the in vivo concentration of BPD, deoxy-hemoglobin (Hb), oxy-hemoglobin (HbO2), total hemoglobin (TotHb), water (H2O) and percent tissue hemoglobin oxygen saturation (%StO2), were calculated from optical property data. PDT efficacy was also determined from morphometric analysis of tumor necrosis in histologic specimens. All the measured tumor properties changed significantly during PDT. [Hb] increased by 9%, while [HbO2], [TotHb] and %StO2 decreased by 18, 7 and 12%, respectively. Using histologic data we show that long-term PDT efficacy is highly correlated to mean BPD concentration in tumor and PDT-induced acute changes in [HbO2], [TotHb] and %StO2 (correlation coefficients of 0.829, 0.817 and 0.953, respectively). Overall, our results indicate that NIR FDPM spectroscopy is able to quantify noninvasively and dynamically the PDT-induced physiological effects in vivo that are highly correlated with therapeutic efficacy. 相似文献
278.
J. W. Eslick Jr H. N. Pham C. Radu A. Puri 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(3):553-562
In this paper, we revisit the problem of quantum entanglement in an
oscillating macroscopic mirror previously studied by Marshall et al. consisting
of a modified Michelson interferometer where one of the mirrors is free to
oscillate about its center of mass. A photon incident upon the oscillating
mirror becomes entangled with the mirror, driving the mirror into a
superposition of quantum states. Once the photon and mirror decouple, the
mirror returns to its initial state. The purpose of our investigations was
to optimize the parameter regime, taking into consideration the current
state of technology and the demands imposed by the need to maintain a stable
environment in the presence of thermal noise. Optimization should not demand
ultra-low temperatures and this is reflected in our results. Our results also
show that if the separation between states is maintained at 10-14 m, the mirror size is reduced, making it easier to induce superposition in
the mirror. The critical nature of mirror reflectivity and its connection to
cavity decay rate was also revealed by our investigations. The results
obtained through our investigations could be useful in quantum error
correction, where decoherence negatively affects the results of computations
performed by quantum computers. Finally, we note that we are only concerned
with an isolated system, where no losses to the external environment occur
and any decoherence that occurs within the system remains internal to the
system; that is, any mention of decoherence refers specifically to
recoverable decoherence. 相似文献
279.
Phan Van Kiem Chau Van Minh Nguyen Xuan Nhiem Nguyen Thi Cuc Ngo Van Quang Hoang Le Tuan Anh Bui Huu Tai Pham Hai Yen Nguyen Thi Hoai Kim Young Ho Nanyoung Kim SeonJu Park Seung Hyun Kim 《Magnetic resonance in chemistry : MRC》2014,52(1-2):51-56
Seven new muurolane‐type sesquiterpenes, (4R,5R)‐muurol‐1(6),10(14)‐diene‐4,5‐diol (1), (4R,5R)‐muurol‐1(6)‐ene‐4,5‐diol (2), (4R,5R,10R)‐10‐methoxymuurol‐1(6)‐ene‐4,5‐diol (3), (4S)‐4‐hydroxy‐1,10‐seco‐muurol‐5‐ene‐1,10‐dione (4), (4R)‐4‐hydroxy‐1,10‐seco‐muurol‐5‐ene‐1,10‐dione (5), (6S,10S)‐6,10‐dihydroxy‐7,8‐seco‐2,8‐cyclo‐muurol‐4(5),7(11)‐diene‐12‐oic acid (6), and (6R,10S)‐6,10‐dihydroxy‐7,8‐seco‐2,8‐cyclo‐muurol‐4(5),7(11)‐diene‐12‐oic acid (7) were isolated from the marine sponge Dysidea cinerea. Their structures were determined by the combination of spectroscopic and chemical methods, including 1D‐NMR, 2D‐NMR, and CD spectra as well as by comparing the NMR data with those reported in the literature. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
280.