首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   14877篇
  免费   2641篇
  国内免费   2176篇
化学   11012篇
晶体学   167篇
力学   854篇
综合类   150篇
数学   1902篇
物理学   5609篇
  2024年   17篇
  2023年   301篇
  2022年   369篇
  2021年   523篇
  2020年   625篇
  2019年   700篇
  2018年   527篇
  2017年   504篇
  2016年   723篇
  2015年   770篇
  2014年   919篇
  2013年   1132篇
  2012年   1361篇
  2011年   1406篇
  2010年   993篇
  2009年   1014篇
  2008年   1039篇
  2007年   879篇
  2006年   815篇
  2005年   665篇
  2004年   561篇
  2003年   448篇
  2002年   513篇
  2001年   387篇
  2000年   321篇
  1999年   334篇
  1998年   261篇
  1997年   226篇
  1996年   197篇
  1995年   176篇
  1994年   145篇
  1993年   155篇
  1992年   101篇
  1991年   99篇
  1990年   84篇
  1989年   81篇
  1988年   70篇
  1987年   39篇
  1986年   39篇
  1985年   47篇
  1984年   28篇
  1983年   18篇
  1982年   24篇
  1981年   11篇
  1979年   7篇
  1978年   6篇
  1977年   5篇
  1976年   4篇
  1973年   3篇
  1972年   4篇
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
991.
A highly efficient strategy for the kinetic resolution of axially chiral BINAM derivatives involving a chiral Brønsted acid‐catalyzed imine formation and transfer hydrogenation cascade process was developed. The kinetic resolution provides a convenient route to chiral BINAM derivatives in high yields with excellent enantioselectivities.  相似文献   
992.
Nanomaterials that combine diagnostic and therapeutic functions within a single nanoplatform are highly desirable for molecular medicine. Herein we report a novel theranostic platform based on a conjugated‐polyelectrolyte (CPE) polyprodrug that contains functionality for image, chemo‐ and photodynamic therapy (PDT), and on‐demand drug release upon irradiation with a single light source. Specifically, the PEGylated CPE serves as a photosensitizer and a carrier, and is covalently conjugated to doxorubicin through a linker that can be cleaved by reactive oxygen species (ROS). Under appropriate light irradiation, the CPE can generate ROS, not only for PDT, but also for on‐demand drug release and chemotherapy. This nanoplatform will offer on‐demand PDT and chemotherapy with drug release triggered by one light switch, which has great potential in cancer treatment.  相似文献   
993.
There is growing consensus that the clinical therapeutic efficacy of some chemotherapeutic agents depends on their off‐target immune‐modulating effects. Pt anticancer drugs have previously been identified to be potent immunomodulators of both the innate and the adaptive immune system. Nevertheless, there has been little development in the rational design of Pt‐based chemotherapeutic agents to exploit their immune‐activating capabilities. The FPR1/2 formyl peptide receptors are highly expressed in immune cells, as well as in many metastatic cancers. Herein, we report a rationally designed multimodal PtIV prodrug containing a FPR1/2‐targeting peptide that combines chemotherapy with immunotherapy to achieve therapeutic synergy and demonstrate the feasibility of this approach.  相似文献   
994.
Polyketide synthases (PKSs) usually employ a ketoreductase (KR) to catalyze the reduction of a β‐keto group, followed by a dehydratase (DH) that drives the dehydration to form a double bond between the α‐ and β‐carbon atoms. Herein, a DH*‐KR* involved in FR901464 biosynthesis was characterized: DH* acts on glyceryl‐S‐acyl carrier protein (ACP) to yield ACP‐linked pyruvate; subsequently KR* reduces α‐ketone that yields L ‐lactyl‐S‐ACP as starter unit for polyketide biosynthesis. Genetic and biochemical evidence was found to support a similar pathway that is involved in the biosynthesis of lankacidins. These results not only identified new PKS domains acting on different substrates, but also provided additional options for engineering the PKS starter pathway or biocatalysis.  相似文献   
995.
The unprecedented title reaction between glycine derivatives and indoles, as well as the auto‐oxidative Povarov/aromatization tandem reaction of glycine derivatives with olefins are described. The reactions were performed in the absence of redox‐active catalysts and chemical oxidants under mild reaction conditions. Only simple organic solvents and air (or O2) were required.  相似文献   
996.
A unique supramolecular two‐component gelation system was constructed from amphiphilic shape‐persistent cyclo[6]aramides and diethylammonium chloride (or triethylammonium chloride). This system has the ability to discriminate native arginine from 19 other amino acids in a specific fashion. Cyclo[6]aramides show preferential binding for the guanidinium residue over ammonium groups. This specificity was confirmed by both experimental results and theoretical simulations. These results demonstrated a new modular displacement strategy, exploring the use of species‐binding hydrogen‐bonded macrocyclic foldamers for the construction of two‐component gelation systems for selective recognition of native amino acids by competitive host–guest interactions. This strategy may be amenable to developing a variety of functional two‐component gelators for specific recognition of various targeted organic molecular species.  相似文献   
997.
Block copolymers comprising thermosensitive poly(N-isopropylacrylamide) (PNIPAM) and hydrophobic poly(n-butyl acrylate) (PBA) blocks, were synthesized using the reversible addition-fragmentation chain transfer polymerization (RAFT), their thermosensitive behavior was studied by ultraviolet spectrophotometer (UV) and dynamic light scattering (DLS). The lower critical solution temperature (LCST) was strongly correlated to the hydrophobic/hydrophilic ratio of the copolymers. Their micellization and self-assembly behavior in dilute aqueous solution were studied by surface tension (SFT), DLS and TEM. The resulting block copolymers reversibly formed or deformed micellar assemblies during their LCSTs. The critical micelle concentration (CMC) was controlled by the composition of PBA and PNIPAM, indicating the successful formation of the block copolymers.  相似文献   
998.
β‐Adrenergic receptors are important targets for drug discovery. We have developed a new β1‐adrenergic receptor cell membrane chromatography (β1AR‐CMC) with offline ultra‐performance LC (UPLC) and MS method for screening active ingredients from traditional Chinese medicines. In this study, Chinese hamster ovary‐S cells with high β1AR expression levels were established and used to prepare a cell membrane stationary phase in a β1AR‐CMC model. The retention fractions were separated and identified by the UPLC–MS system. The screening results found that isoimperatorin from Rhizoma et Radix Notopterygii was the targeted component that could act on β1AR in similar manner of metoprolol as a control drug. In addition, the biological effects of active component were also investigated in order to search for a new type of β1AR antagonist. It will be a useful method for drug discovery as a leading compound resource.  相似文献   
999.
Porous CuO micro‐/nanostructures with clean surface, prepared through Cu2(OH)2CO3 precursor followed by calcination in air, were proven to be an effective peroxidase mimic. They can quickly catalyze oxidation of the peroxidase substrate 3,3′,5,5′‐tetramethylbenzidine (TMB) in the presence of H2O2, producing a blue color. The obtained porous CuO micro‐/nanostructure have potential application in wastewater treatment. The apparent steady‐state kinetic parameter was studied with TMB as the substrate. In addition, the potential application of the porous CuO in wastewater treatment was demonstrated with phenol‐containing water as an example. Such investigation not only confirms the intrinsic peroxidase‐like activity of micro‐/nanostructured CuO, but also suggests its potential application in wastewater treatment.  相似文献   
1000.
A series of novel chelating fibers containing sulfur, nitrogen, oxygen heteroatoms were prepared via the functionalization of chloromethylated polyphenylene sulfide (CMPPS). The structures, micromorpholo- gy and physicochemical properties of these fibrous adsorptive materials were characterized by FT-IR, elementary analysis, TG and SEM-EDS. The results show that chelating fibers had high functional group contents (3.94 mmol/g for thiourea, 3.85 mmol/g for mercapto, 5.00 mmol/g for methylamine and 6.07 mmol/g for ethylenediamine, respectively). Owing to the unique matrix of polyphenylene sulfide fiber, these fibrous adsorbents possess excellent thermostability. This synthetic method proved a simple and efficient way for the preparation of chelating fibers.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号