全文获取类型
收费全文 | 27691篇 |
免费 | 4365篇 |
国内免费 | 4096篇 |
专业分类
化学 | 21191篇 |
晶体学 | 440篇 |
力学 | 1358篇 |
综合类 | 307篇 |
数学 | 3011篇 |
物理学 | 9845篇 |
出版年
2024年 | 96篇 |
2023年 | 503篇 |
2022年 | 960篇 |
2021年 | 1060篇 |
2020年 | 1098篇 |
2019年 | 1161篇 |
2018年 | 979篇 |
2017年 | 1011篇 |
2016年 | 1335篇 |
2015年 | 1375篇 |
2014年 | 1709篇 |
2013年 | 2121篇 |
2012年 | 2551篇 |
2011年 | 2603篇 |
2010年 | 1990篇 |
2009年 | 1880篇 |
2008年 | 1987篇 |
2007年 | 1827篇 |
2006年 | 1728篇 |
2005年 | 1374篇 |
2004年 | 1014篇 |
2003年 | 795篇 |
2002年 | 757篇 |
2001年 | 659篇 |
2000年 | 585篇 |
1999年 | 489篇 |
1998年 | 365篇 |
1997年 | 327篇 |
1996年 | 279篇 |
1995年 | 266篇 |
1994年 | 237篇 |
1993年 | 172篇 |
1992年 | 149篇 |
1991年 | 146篇 |
1990年 | 122篇 |
1989年 | 92篇 |
1988年 | 75篇 |
1987年 | 54篇 |
1986年 | 65篇 |
1985年 | 51篇 |
1984年 | 21篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1971年 | 4篇 |
1957年 | 4篇 |
1936年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Seifert N Liu D Barnes A Albridge R Yan Q Tolk N Husinsky W Betz G 《Physical review. B, Condensed matter》1993,47(13):7653-7658
82.
叙述了用θ-2θ型X射线衍射仪精确测定电解质溶液结构的新实验技术。设计制作了具有恒温功能的超厚液体样品池,并建立了样品池窗口强度的校正方法。优化了液体X射线衍射数据和结构参数精细化的计算机程序,获得了非常令人满意的实验结果。由θ-2θ型X射线衍射仪精确测定的径向分布函数与θ-θ型衍射仪自由散射比较,表明DRF分辨率有所提高。 相似文献
83.
Three kinds of nylon 10 14 crystals with different perfections were prepared under various crystallization conditions. The Brill transition behavior of these nylon 10 14 crystals was investigated by variable-temperature X-ray diffraction. It was found that the crystallization conditions influence the Brill transition temperature greatly. The Brill transition temperature of the lamellar crystals grown from dilute solution is so high that no Brill transition temperature can be observed before melting. However, for crystals postannealed at 125 °C, the Brill transition temperature is as low as 130 °C. The results show that the Brill transition behavior of nylons is strongly dependent on the crystallization conditions, for example, the perfections of the crystals. 相似文献
84.
Yan Shaozong 《数学年刊B辑(英文版)》1984,5(1):91-100
The spectral theory of selfadjoint operators and unitary operators in Hilbert space has been successfully generalized to $\[{\Pi _k}\]$ space. However, there are only a few results for the spectral theory of selfadjoint operators and unitary operators in $\[\Pi \]$ space. One of the important reasons is that the structure of $\[\Pi \]$ space is more complex than that of $\[{\Pi _k}\]$ space. This paper and the forthcoming paper "The structure of $\[\Pi \]$ space (II)" will mainly be dealt with the structure of $\[\Pi \]$ spaces, which will be used to further study the operators in $\[\Pi \]$ spaces. 相似文献
85.
Ai‐Hua Zhao Yan Zhang Zhao‐Hui Xu Jian‐Wen Liu Wei Jia 《Helvetica chimica acta》2004,87(12):3160-3166
Three new enmein‐type ent‐kaurenoids, i.e., the two pairs 1 and 2 of 20‐epimers and the (20R)‐isomer 3 , besides the seven known diterpenoids 4 – 10 , were isolated from the aerial parts of Isodon serra. Their structures were elucidated by spectroscopic techniques and X‐ray diffraction. The immunosuppressive effect for T‐lymphocytes proliferation induced by Con A in BALB/c mouse was evaluated for the isolates 1 – 10 . They all displayed a remarkable inhibitory effect, with multi‐glycosides of Tripterygium wilfordii as positive reference substance (Table 3). 相似文献
86.
A new series of MR-IPN polyacrylamide—poly(vinyl-ethylenediamine)chelatesorbents were prepared by the reaction of ethylenediamine with MR-IPN matrixes.The newchelate sorbent showed good sorption properties for auric and platinic ions. 相似文献
87.
Adsorption of NH3 onto activated carbon prepared from palm shells impregnated with H2SO4 总被引:3,自引:0,他引:3
Adsorption of ammonia (NH3) onto activated carbons prepared from palm shells impregnated with sulfuric acid (H2SO4) was investigated. The effects of activation temperature and acid concentration on pore surface area development were studied. The relatively large micropore surface areas of the palm-shell activated carbons prepared by H2SO4 activation suggest their potential applications in gas adsorption. Adsorption experiments at a fixed temperature showed that the amounts of NH3 adsorbed onto the chemically activated carbons, unlike those prepared by CO2 thermal activation, were not solely dependent on the specific pore surface areas of the adsorbents. Further adsorption tests for a wide range of temperatures suggested combined physisorption and chemisorption of NH3. Desorption tests at the same temperature as adsorption and at an elevated temperature were carried out to confirm the occurrence of chemisorption due to the interaction between NH3 and some oxygen functional groups via hydrogen bonding. The surface functional groups on the adsorbent surface were detected by Fourier transform infrared spectroscopy. The amounts of NH3 adsorbed by chemisorption were correlated with the contents of elemental oxygen present in the adsorbents. Mechanisms for chemical activation and adsorption processes are proposed based on the observed phenomena. 相似文献
88.
Allylic hydroxy phosphonates and their derivatives can be interconverted by using cross metathesis with second generation Grubbs catalyst. The absolute stereochemistry of the starting phosphonate is conserved in the product. Cross metathesis reaction of the acrolein-derived phosphonate 2a yields a series of functionalized allylic hydroxy phosphonates. However, the cross metathesis reaction is often accompanied by competing dimerization and alkene migration reactions leading to a reduction in yield. The cinnamaldehyde- and crotonaldehyde-derived phosphonates 2b and 2c were also examined. In general, the metathesis reactions of phosphonates 2b and 2c are considerably slower than those for phosphonate 2a leading to mixtures. Several hydroxyl-protected derivatives of the phosphonate 2a (methyl carbonate 3a, acetate 4a, N-tosyl carbamate 5a, TBDMS 6a, and acetoacetate 7a) undergo metathesis without competing side reactions to give substituted allylic phosphonates in good to excellent yield. 相似文献
89.
Yan Shaozong 《数学年刊B辑(英文版)》1980,1(34):485-499
Let H be a Hilbert space, and let A be a linear bounded operator on H. For
\(\lambda \in \rho (A)\), the \({U_\lambda } = {(A - \lambda )^{ * - 1}}(A - \lambda )\) is called polar.Produot operator.
In this paper, we discuss the properties of \({U_\lambda }\) and the relation between \({U_\lambda }\) and A. We obtain tbe following results.
Definition. Let B be a linear bounded operator on H, suppose \(0 \in \rho (B)\). For every
\(x,y \in H\), we definite \([x,y] = (Bx,y)(H,B)\)(or (H, [·,·]) is called a non-
degenerate bilinear space (it is obvious that if B=B*,then (H,B)is a space with an
indefinite metric; and that if B>0, then (H,B) is a Hilbert Space. If an operator
U(A) satisfies
\[[Ux,Uy] = [x,y]([Ax,y] = [x,Ay]),x,y \in H\]
then the operator U(A) is called a wvitary (self adjoint) on (H,B).
Theorem I . Suppose A is a linear bounded operator on H,
(1) If \(0 \in \rho (A)\), then \(U = {A^{ * - 1}}A\) is a unitary operator on (H,A) or (H, A*), and \(\sigma (U) = \frac{1}{{\sigma (U)}}\).
(2) If there is a complex number \(\alpha \), such that \({\mathop{\rm Im}\nolimits} A \ge \alpha > 0\) then a)\(0 \in \rho (A)\), and
the operator \(U = {A^{ * - 1}}A\) is a unitary on Hilbert space \((H,{\mathop{\rm Im}\nolimits} A) and 1 \in \rho (U)\);b) there exist two Hilbert spaces \((H,{v_1}),(H,{v_2})\), such that A, A* are all the unitary operator
from (H,v1) onto (H,v2), and there are two spectral measures \(\{ E_\lambda ^i,\lambda \in [\alpha ,\chi ] \subset (0,2\pi )\} ,i = 1,2,\), such that \(AE_\Delta ^1H \subset E_\Delta ^2H,{A^ * }E_\Delta ^1H \subset E_\Delta ^2H\) for any \(\Delta = (\lambda ,u] \subset (0,2\pi ]\).
(3) If \(0 \in \rho (A) \cap \rho ({\mathop{\rm Im}\nolimits} A)\) then the operator \(U = {A^{ * - 1}}A\) is a unitary on \((H,{\mathop{\rm Im}\nolimits} A)\).
with an indefinite met He, and \(1 \in \rho (U)\).
(4) For any complex number \(\lambda = r{e^{i\theta }},\left| \lambda \right| > \left\| A \right\|\), then \({U_\lambda }\) must be a unitary operator on the Hilbert space \(\left( {H,{\mathop{\rm Im}\nolimits} (\frac{1}{{i\lambda }}A + iI)} \right),and - {e^{i2\theta }} \in \rho ({U_\lambda })\)
Theorem 2. (1) A is a normal operator iff there exists a complex number \(\lambda \),
\(\lambda \in \rho (A)\), such that \(\frac{{\partial {U_\lambda }}}{{\partial \lambda }}{U_\lambda } = {U_\lambda }\frac{{\partial {U_\lambda }}}{{\partial \lambda }}\),where \(\frac{\partial }{{\partial \lambda }}\) is the directional derivative.
(2) If there exists a complex number \(\alpha ,{\mathop{\rm Im}\nolimits} A \ge \alpha > 0\) then A is a normal operator
iff \(U = {A^{ * - 1}}A\) is also.
(3) If A is a hyperiwrmal or a subnormal, then for every \(\lambda \in \rho (A),\sigma ({U_\lambda })\) lies on the circle.
3, 4期
关于极?积算子炉一U
499
Theorem 3? Let A be a linear bounded operator on Hm Suppose 0£p(J.)?
(1) If U=А*~гА is a unitary operator in a certain non-degenerate bilinear space
(H} 1 J |Л|>1 入 J Ш=1
solmble iff (l)cr(ü) =-=i=-, (2) the operotor Ui= f XdE\ is unitarity equivalent to
cr(C7) J |л|>1
the operator ül_1 == ШЕ1, 、
J 1Л|>1
If the conditions (1),(2) are satified, then we have
(3) the subspace JJi?^2 of H reduces any solution of the equation A*"1 A — U, and
1
AI (Ягея*)1 = ^Uo where Ъ is any in vertible self-adjoint on (i?i?J?2) L, and bv Uo
(Uo = Jiai i ЫЕ1 )}⑷41Я1фя, = , Ла = A1ü2, if the operator V is to
realize TJt and Ut^unitary equivalence^ then Ai = VSf where S is any invertible on Нг
and SvUi. "
Corollary. Swpp)se operator U is a normal on a certain Hilbert space(Hy v) (^the
U is similar to a certain normal operator on IT), if U satisfies the conditions (1)、(2) of
Theorem^ on ?S,v) ? Then the general form of the solution of А*~гА = U is A = vA'y
where A' is same as A in Theorem^.
Theorem 5. Let U be a linear bounded operator on H. Suppose O?p(J.)and p(ü)
is a simply connected region, then the equation А*~гЛ = U is a solvable iff there
exists a certain space {H,v) with a indefinite metric, such that U is a unitary operator
on (Hf 丨).
If is a unitary operator on ?H,v),then there exists a particular solution of
I X+$
А*~гА = U: Ar = 2e v [ (?7 —X)_1+X], where eie ? p (JJ), and the general form of the
solution is Аж АУ, wliere V is any in vertible self-adjoint on (H, -u)and VvU, 相似文献
90.
Zi-Shu Yang Yuhang Yao Adam C. Sedgwick Cuicui Li Ye Xia Yan Wang Lei Kang Hongmei Su Bing-Wu Wang Song Gao Jonathan L. Sessler Jun-Long Zhang 《Chemical science》2020,11(31):8204
We report here porphodilactol derivatives and their corresponding metal complexes. These systems show promise as “all-in-one” phototheranostics and are predicated on a design strategy that involves controlling the relationship between intersystem crossing (ISC) and photothermal conversion efficiency following photoexcitation. The requisite balance was achieved by tuning the aromaticity of these porphyrinoid derivatives and forming complexes with one of two lanthanide cations, namely Gd3+ and Lu3+. The net result led to a metalloporphodilactol system, Gd-trans-2, with seemingly optimal ISC efficiency, photothermal conversion efficiency and fluorescence properties, as well as good chemical stability. Encapsulation of Gd-trans-2 within mesoporous silica nanoparticles (MSN) allowed its evaluation for tumour diagnosis and therapy. It was found to be effective as an “all-in-one” phototheranostic that allowed for NIR fluorescence/photoacoustic dual-modal imaging while providing an excellent combined PTT/PDT therapeutic efficacy in vitro and in vivo in 4T1-tumour-bearing mice.We report here porphodilactol derivatives and their corresponding metal complexes as “all-in-one” phototheranostics by controlling the relationship between intersystem crossing (ISC) and photothermal conversion efficiency following photoexcitation. 相似文献