全文获取类型
收费全文 | 2196篇 |
免费 | 46篇 |
国内免费 | 12篇 |
专业分类
化学 | 1477篇 |
晶体学 | 17篇 |
力学 | 39篇 |
数学 | 287篇 |
物理学 | 434篇 |
出版年
2021年 | 26篇 |
2020年 | 24篇 |
2019年 | 32篇 |
2018年 | 22篇 |
2017年 | 18篇 |
2016年 | 52篇 |
2015年 | 34篇 |
2014年 | 28篇 |
2013年 | 96篇 |
2012年 | 102篇 |
2011年 | 139篇 |
2010年 | 65篇 |
2009年 | 59篇 |
2008年 | 127篇 |
2007年 | 125篇 |
2006年 | 141篇 |
2005年 | 94篇 |
2004年 | 92篇 |
2003年 | 76篇 |
2002年 | 85篇 |
2001年 | 42篇 |
2000年 | 35篇 |
1999年 | 16篇 |
1998年 | 29篇 |
1997年 | 29篇 |
1996年 | 31篇 |
1995年 | 21篇 |
1994年 | 24篇 |
1993年 | 26篇 |
1992年 | 24篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 14篇 |
1988年 | 26篇 |
1987年 | 31篇 |
1986年 | 14篇 |
1985年 | 48篇 |
1984年 | 34篇 |
1983年 | 22篇 |
1982年 | 35篇 |
1981年 | 27篇 |
1980年 | 25篇 |
1979年 | 37篇 |
1978年 | 18篇 |
1977年 | 22篇 |
1976年 | 19篇 |
1975年 | 18篇 |
1974年 | 15篇 |
1972年 | 14篇 |
1970年 | 13篇 |
排序方式: 共有2254条查询结果,搜索用时 125 毫秒
101.
102.
103.
Dr. Roman S. Erdmann Dr. Hideo Takakura Alexander D. Thompson Felix Rivera‐Molina Dr. Edward S. Allgeyer Prof. Dr. Joerg Bewersdorf Prof. Dr. Derek Toomre Prof. Dr. Alanna Schepartz 《Angewandte Chemie (International ed. in English)》2014,53(38):10242-10246
We report a lipid‐based strategy to visualize Golgi structure and dynamics at super‐resolution in live cells. The method is based on two novel reagents: a trans‐cyclooctene‐containing ceramide lipid (Cer‐TCO) and a highly reactive, tetrazine‐tagged near‐IR dye (SiR‐Tz). These reagents assemble via an extremely rapid “tetrazine‐click” reaction into Cer‐SiR, a highly photostable “vital dye” that enables prolonged live‐cell imaging of the Golgi apparatus by 3D confocal and STED microscopy. Cer‐SiR is nontoxic at concentrations as high as 2 μM and does not perturb the mobility of Golgi‐resident enzymes or the traffic of cargo from the endoplasmic reticulum through the Golgi and to the plasma membrane. 相似文献
104.
Fan Shi Aaron M. Coffey Assist. Prof. Kevin W. Waddell Assist. Prof. Eduard Y. Chekmenev Assoc. Prof. Boyd M. Goodson 《Angewandte Chemie (International ed. in English)》2014,53(29):7495-7498
A novel variant of an iridium‐based organometallic catalyst was synthesized and used to enhance the NMR signals of pyridine in a heterogeneous phase by immobilization on polymer microbead solid supports. Upon administration of parahydrogen (pH2) gas to a methanol mixture containing the HET‐SABRE catalyst particles and the pyridine, up to fivefold enhancements were observed in the 1H NMR spectra after sample transfer to high field (9.4 T). Importantly, enhancements were not due to any residual catalyst molecules in solution, thus supporting the true heterogeneity of the SABRE process. Further significant improvements may be expected by systematic optimization of experimental parameters. Moreover, the heterogeneous catalyst is easy to separate and recycle, thus opening a door to future potential applications varying from spectroscopic studies of catalysis, to imaging metabolites in the body without concern of contamination from expensive and potentially toxic metal catalysts or accompanying organic molecules. 相似文献
105.
Lijun Zhou Derek K. O'Flaherty Jack W. Szostak 《Angewandte Chemie (International ed. in English)》2020,59(36):15682-15687
The non‐enzymatic replication of the primordial genetic material is thought to have enabled the evolution of early forms of RNA‐based life. However, the replication of oligonucleotides long enough to encode catalytic functions is problematic due to the low efficiency of template copying with mononucleotides. We show that template‐directed ligation can assemble long RNAs from shorter oligonucleotides, which would be easier to replicate. The rate of ligation can be greatly enhanced by employing a 3′‐amino group at the 3′‐end of each oligonucleotide, in combination with an N‐alkyl imidazole organocatalyst. These modifications enable the copying of RNA templates by the multistep ligation of tetranucleotide building blocks, as well as the assembly of long oligonucleotides using short splint oligonucleotides. We also demonstrate the formation of long oligonucleotides inside model prebiotic vesicles, which suggests a potential route to the assembly of artificial cells capable of evolution. 相似文献
106.
Derek C. Church Jonathan K. Pokorski 《Angewandte Chemie (International ed. in English)》2020,59(28):11379-11383
Cell‐based therapies are gaining prominence in treating a wide variety of diseases and using synthetic polymers to manipulate these cells provides an opportunity to impart function that could not be achieved using solely genetic means. Herein, we describe the utility of functional block copolymers synthesized by ring‐opening metathesis polymerization (ROMP) that can insert directly into the cell membrane via the incorporation of long alkyl chains into a short polymer block leading to non‐covalent, hydrophobic interactions with the lipid bilayer. Furthermore, we demonstrate that these polymers can be imbued with advanced functionalities. A photosensitizer was incorporated into these polymers to enable spatially controlled cell death by the localized generation of 1O2 at the cell surface in response to red‐light irradiation. In a broader context, we believe our polymer insertion strategy could be used as a general methodology to impart functionality onto cell‐surfaces. 相似文献
107.
Two Ru(II) complexes, [Ru(bpy)2L](ClO4)2 (1) and [Ru(bpy)2L'](BF4)2 (2), where bpy is 2,2'-bipyridine, L is diacetyl dihydrazone, and L' 1:2 is the condensate of L and acetone, are synthesized. From X-ray crystal structures, both are found to contain distorted octahedral RuN(6)(2+) cores. NMR spectra show that the cations in 1 and 2 possess a C2 axis in solution. They display the expected metal-to-ligand charge transfer (1MLCT) band in the 400-500 nm region. Complex 1 is nonemissive at room temperature in solution as well as at 80 K. In contrast, complex 2 gives rise to an appreciable emission upon excitation at 440 nm. The room-temperature emission is centered at 730 nm (lambda(em)(max)) with a quantum yield (Phi(em)) of 0.002 and a lifetime (tau(em)) of 42 ns in an air-equilibrated methanol-ethanol solution. At 80 K, Phi(em) = 0.007 and tau(em) = 178 ns, with a lambda(em)(max) of 690 nm, which is close to the 0-0 transition, indicating an 3MLCT excited-state energy of 1.80 eV. The radiative rate constant (5 x 10(4) s(-1)) at room temperature and 80 K is almost temperature independent. From spectroelectrochemistry, it is found that bpy is easiest to reduce in 2 and that L is easiest in 1. The implications of this are that in 2 the lowest (3)MLCT state is localized on a bpy ligand and in 1 it is localized on L. Transient absorption results also support these assignments. As a consequence, even though 2 shows a fairly strong and long-lived emission from a Ru(II) --> bpy CT state, the Ru(II) --> L CT state in 1 shows no detectable emission even at 80 K. 相似文献
108.
We report liquid chromatographic separation with tandem mass spectrometry determination of 12 endogenous estrogens and their intact conjugates in blood and urine and its application to study effects of exemestane treatment on estrogen generation and metabolism in postmenopausal women with estrogen-dependent breast cancer. A 0.5 mL aliquot of each urine or serum sample is fractionated with solid phase extraction to a fraction of free estrogen and another fraction of their conjugates. The reversed phase LC/MS/MS determines dansylated estrogens with positive ionization and intact conjugates with negative ionization. The method provides reproducible separation and limit of detection as low as 1 pg mL−1 for free estrogens and 0.03 ng mg−1 creatinine for the conjugates in serum and urine samples. The method enabled us to acquire unique concentration profiles of 12 endogenous estrogens and their intact conjugates in 30 breast cancer patients before and after one month of exemestane treatment. Exemestane suppressed total serum and urinary estrogens by 11–97% (P < 0.0001) and 8.7–91% (P < 0.0001), respectively. Specifically, these data show that exemestane preferentially suppressed E1, E1-3S, E1-3G, and E2-17G more than other estrogens. Linear regression analysis of estrogen concentrations before and after treatment showed correlation coefficients of 0.8385 (n = 289, P < 0.0001) and 0.8863 (n = 360, P < 0.0001). This study provides urinary and blood estrogen concentration profiles in breast cancer patients to demonstrate the effect of exemestane on estrogen generation, supporting inhibition of aromatase activity. 相似文献
109.
A Scalable Biomimetic Synthesis of Resveratrol Dimers and Systematic Evaluation of their Antioxidant Activities
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Bryan S. Matsuura Mitchell H. Keylor Bo Li YuXuan Lin Shelby Allison Prof. Dr. Derek A. Pratt Prof. Dr. Corey R. J. Stephenson 《Angewandte Chemie (International ed. in English)》2015,54(12):3754-3757
An efficient synthetic route to the resveratrol oligomers quadrangularin A and pallidol is reported. It features a scalable biomimetic oxidative dimerization that proceeds in excellent yield and with complete regioselectivity. A systematic evaluation of the natural products and their synthetic precursors as radical‐trapping antioxidants has revealed that, contrary to popular belief, this mode of action is unlikely to account for their observed biological activity. 相似文献
110.
T. F. Watson D. Belić P. Y. Convers E. J. Boyd S. A. Brown 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,61(1):81-85
Thin films produced by depositing tin clusters with sizes between 5 and 10 nm onto silicon nitride substrates were found to
be
highly coalesced resulting in grains with sizes ~30 nm. Exposing the clusters to nitrogen before they were deposited significantly
reduced the coalescence between them and resulted in granular films where the clusters mostly retained their shape. This is
due to a small
amount of tin nitride forming in the clusters. The coalesced and granular films were used to fabricate tin oxide gas sensors.
This was
done by depositing the two types of films onto silicon nitride chips and then oxidising them by baking at 250 °C for 24 h.
It was found that the sensors composed of uncoalesced clusters were much more sensitive to hydrogen. This was attributed to
the smaller grain size and the larger surface area of the granular films. 相似文献