全文获取类型
收费全文 | 1653篇 |
免费 | 48篇 |
国内免费 | 6篇 |
专业分类
化学 | 960篇 |
晶体学 | 16篇 |
力学 | 23篇 |
数学 | 286篇 |
物理学 | 274篇 |
无线电 | 148篇 |
出版年
2020年 | 19篇 |
2019年 | 25篇 |
2016年 | 26篇 |
2015年 | 18篇 |
2014年 | 25篇 |
2013年 | 40篇 |
2012年 | 56篇 |
2011年 | 47篇 |
2010年 | 45篇 |
2009年 | 52篇 |
2008年 | 59篇 |
2007年 | 55篇 |
2006年 | 46篇 |
2005年 | 55篇 |
2004年 | 48篇 |
2003年 | 37篇 |
2002年 | 31篇 |
2001年 | 23篇 |
2000年 | 28篇 |
1999年 | 26篇 |
1998年 | 14篇 |
1997年 | 20篇 |
1996年 | 24篇 |
1995年 | 15篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 24篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 15篇 |
1988年 | 15篇 |
1987年 | 18篇 |
1985年 | 23篇 |
1984年 | 17篇 |
1983年 | 14篇 |
1980年 | 14篇 |
1978年 | 13篇 |
1973年 | 13篇 |
1960年 | 12篇 |
1956年 | 16篇 |
1934年 | 26篇 |
1933年 | 15篇 |
1932年 | 29篇 |
1931年 | 24篇 |
1930年 | 21篇 |
1929年 | 13篇 |
1928年 | 16篇 |
1926年 | 23篇 |
1923年 | 19篇 |
1922年 | 16篇 |
排序方式: 共有1707条查询结果,搜索用时 312 毫秒
921.
922.
Dr. Isabelle Marie Daubit Svenja Wortmann Dr. Daniel Siegmund Prof. Dr. Stephan Hahn Prof. Dr. Patrick Nuernberger Prof. Dr. Nils Metzler-Nolte 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(22):6783-6794
Complexes of RhI and IrI of the [M(COD)(NHC)X] type (where M=Rh or Ir, COD=1,5-cyclooctadiene, NHC=N-heterocyclic carbene, and X=halide) have recently shown promising cytotoxic activities against several cancer cell lines. Initial mechanism of action studies provided some knowledge about their interaction with DNA and proteins. However, information about their cellular localization remains scarce owing to luminescence quenching within this complex type. Herein, the synthesis of two rare examples of luminescent RhI and IrI [M(COD)(NHC)I] complexes with 1,8-naphthalimide-based emitting ligands is reported. All new complexes are comprehensively characterized, including with single-crystal X-ray structures. Steric crowding in one derivative leads to two distinct rotamers in solution, which apparently can be distinguished both by pronounced NMR shifts and by their respective spectral and temporal emission signatures. When the photophysical properties of these new complexes are exploited for cellular imaging in HT-29 and PT-45 cancer cell lines, it is demonstrated that the complexes accumulate predominantly in the endoplasmic reticulum, which is an entirely new finding and provides the first insight into the cellular localization of such IrI(NHC) complexes. 相似文献
923.
924.
925.
Marcus Lederer Dr. Uwe Hahn Javier Fernández‐Ariza Olga Trukhina Dr. M. Salomé Rodríguez‐Morgade Claudia Dammann Prof. Thomas Drewello Prof. Tomás Torres Prof. Dirk M. Guldi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5916-5925
A zinc phthalocyanine endowed with four [18]‐crown‐6 moieties, ZnPcTeCr, has been prepared and self‐assembled with either pyridyl‐functionalized perylenebisimides (PDI‐Py) or fullerenes (C60‐Py) to afford a set of novel electron donor–acceptor hybrids. In the case of ZnPcTeCr, aggregation has been circumvented by the addition of potassium or rubidium ions to lead to the formation of monomers and cofacial dimers, respectively. From fluorescence titration experiments, which gave rise to mutual interactions between the electron donors and the acceptors in the excited state, the association constants of the respective ZnPcTeCr monomers and/or dimers with the corresponding electron acceptors were derived. Complementary transient‐absorption experiments not only corroborated photoinduced electron transfer from ZnPcTeCr to either PDI‐Py or C60‐Py within the electron donor–acceptor hybrids, but also the unexpected photoinduced electron transfer within ZnPcTeCr dimers. In the electron donor–acceptor hybrids, the charge‐separated‐state lifetimes were elucidated to be close to 337 ps and 3.4 ns for the two PDI‐Pys, whereas the longest lifetime for the photoactive system that contains C60‐Py was calculated to be approximately 5.1 ns. 相似文献
926.
In a previous publication, numerous different 3D printing technologies were reviewed, projection‐based temporal‐focusing 3D printing being one of them. There, one condensed paragraph is dedicated to discussing the proximity effect for said 3D printing approach, based on a publication by Saha et al. (2019). In a comment, Saha and Chen (2020) criticized the discussion on projection‐based temporal‐focusing 3D printing. In this response, the discussion on the proximity effect is expanded and aspects addressed in the comment by Saha and Chen (2020) are clarified. 相似文献
927.
The objective of this study was to assess the amount of energy transferred to the backing material of oil-based clay (i.e. kinetic dissipation) in ballistic tests of soft body armor panels. To determine the relationship between penetration depth (or dent volume) and impact velocity (or energy), weight dropping test with a series of steel spheres was carried out at low impact velocities, and direct shooting with a 5.56 mm NATO fragment simulating projectile (FSP) was carried out at high impact velocities. At high and low impact velocities, the volume of the dent made in the oil-based clay was proportional to the velocity of the impactor. The change in dent volume per the change in impact velocity was found to be proportional to the 1.5th power of the mass of the impactor, while the energy absorption per unit dent volume increased linearly with the impact velocity. The relationship between trauma depth (or dent volume) and kinetic dissipation of a soft body armor panel subjected to a 9 mm bullet at 436 m/s is presented, where the trauma diameter approached that of a 1.043 kg steel ball. 相似文献
928.
Bilge Baytekin Dr. H. Tarik Baytekin Dr. Uwe Hahn Dr. Werner Reckien Dr. Barbara Kirchner Prof. Dr. Christoph A. Schalley Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(29):7139-7149
The mass spectrometric characterization of Fréchet‐type dendrons is reported. In order to provide the charges necessary for electrospray ionization, dendrons bearing an OH group at the focal point can be deprotonated and observed in the negative ion mode. Alternatively, the corresponding bromides can be converted to quaternary ammonium ions that can easily be detected in the positive mode. If the latter ions are subjected to collision‐induced dissociation experiments, a fragmentation cascade begins with the dissociation of the focal amine. The focal benzyl cation quickly decomposes in a fragmentation cascade from the focal point to the periphery until the peripheral benzyl (or naphthylmethyl) cations are formed. Five different mechanisms are discussed in detail, three of which can be excluded based on experimental evidence. The cascade fragmentation is reminiscent of self‐immolative dendrimers. 相似文献
929.
We show that the demand for news varies with the perceived affinity of the news organization to the consumer's political preferences. In an experimental setting, conservatives and Republicans preferred to read news reports attributed to Fox News and to avoid news from CNN and NPR. Democrats and liberals exhibited exactly the opposite syndrome—dividing their attention equally between CNN and NPR, but avoiding Fox News. This pattern of selective exposure based on partisan affinity held not only for news coverage of controversial issues but also for relatively "soft" subjects such as crime and travel. The tendency to select news based on anticipated agreement was also strengthened among more politically engaged partisans. Overall, these results suggest that the further proliferation of new media and enhanced media choices may contribute to the further polarization of the news audience. 相似文献
930.
This paper considers passive fund selection from an individual investor's perspective. The growth of the passive fund market over the past decade is staggering. Individual investors who wish to buy these funds for their retirement and brokerage accounts have many options and are faced with a difficult selection problem. Which funds do they invest in, and in what proportions? We develop a novel statistical methodology to address this problem by adapting recent advances in posterior summarization. A Bayesian decision‐theoretic approach is presented to construct optimal sparse portfolios for individual investors over time. 相似文献