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   2222篇
  免费   163篇
  国内免费   94篇
化学   958篇
晶体学   5篇
力学   43篇
数学   30篇
物理学   1443篇
  2024年   4篇
  2023年   14篇
  2022年   23篇
  2021年   30篇
  2020年   34篇
  2019年   39篇
  2018年   36篇
  2017年   52篇
  2016年   53篇
  2015年   65篇
  2014年   80篇
  2013年   98篇
  2012年   118篇
  2011年   153篇
  2010年   151篇
  2009年   158篇
  2008年   146篇
  2007年   180篇
  2006年   128篇
  2005年   120篇
  2004年   87篇
  2003年   82篇
  2002年   67篇
  2001年   40篇
  2000年   37篇
  1999年   41篇
  1998年   36篇
  1997年   43篇
  1996年   30篇
  1995年   23篇
  1994年   32篇
  1993年   34篇
  1992年   21篇
  1991年   22篇
  1990年   31篇
  1989年   21篇
  1988年   29篇
  1987年   21篇
  1986年   26篇
  1985年   12篇
  1984年   5篇
  1983年   3篇
  1982年   13篇
  1981年   9篇
  1980年   4篇
  1979年   5篇
  1978年   8篇
  1976年   3篇
  1973年   4篇
  1972年   2篇
排序方式: 共有2479条查询结果,搜索用时 15 毫秒
1.
2.
Endocytosis plays important roles in many cellular physiological processes, such as metabolism and immune. Many theoretical models have been proposed to study the endocytic process, but little has considered the tensile deformation of the membrane and the actin forces. In this paper, a new endocytic model is proposed based on the co-rotational grid method. Our model gives a direct estimation of the in-plane strain of the plasma membrane and provides a basis for the calculation of further scission process of the vesicle. The results fit well with experimental data in the literature. Moreover, it is suggested that the active forces of actin at the endocytic site is the main mechanism driving the invagination of the plasma membrane.  相似文献   
3.
A polyimide containing alicyclic sequences was synthesized by a two steps solution polycondensation reaction and further processed into the film form for antibacterial purposes. The sample surface was activated by RF plasma treatment to ensure the biocide attachment by immersion in by NaOH/AgNO3 solution. Surface properties of the synthesized polyimide film were analyzed by FTIR, contact angle and atomic force microscopy measurements, before and after the treatments with plasma and silver-based biocide. Antibacterial tests revealed that the pristine sample inhibit the growth of Staphylococcus aureus ATCC 25923 and Escherichia coli ATCC 25922, and this behavior is more pronounced after the biocide surface treatment. The differences in the biocidal activity were discussed in terms of sample and bacteria hydrophobic/hydrophilic interactions.  相似文献   
4.
《Physics letters. A》2020,384(4):126101
Classical electromagnetism with magnetic monopoles is not a Hamiltonian field theory because the Jacobi identity for the Poisson bracket fails. The Jacobi identity is recovered only if all of the species have the same ratio of electric to magnetic charge or if an electron and a monopole can never collide. Without the Jacobi identity, there are no local canonical coordinates or Lagrangian action principle. To build a quantum field of magnetic monopoles, we either must explain why the positions of electrons and monopoles can never coincide or we must resort to new quantization techniques.  相似文献   
5.
Solid-state batteries (SSBs) that use solid electrolytes instead of flammable liquid electrolytes have the potential to generate higher specific capacity and offer better safety. Magnesium (Mg) based SSBs with Mg metal anodes are considered to be one of the most promising energy storage candidates, because it gives high theoretical volumetric capacities of 3830 mAh cm−3. Here, we demonstrate an atomic layer deposition (ALD) process with a double nitrogen plasma process that successfully produces nitrogen-incorporated magnesium phosphorus oxynitride (MgPON) solid-state electrolyte (SSE) thin films at a low deposition temperature of 125 °C. The ALD MgPON SSEs exhibit an ionic conductivity of 0.36 and 1.2 μS cm−1 at 450 and 500 °C, respectively. The proposed ALD strategy shows the ability of conformal deposition nitrogen-doped SSEs on pattered substrates and is attractive for using nitride ion-conducing films as protective or wetting interlayers in solid-state Mg and Li batteries.  相似文献   
6.
石膏在我国储量丰富,应用广泛,快速准确分析其成分含量对石膏资源的综合利用具有重要意义。针对酸溶法无法测定SiO2,碱熔法无法测定K2O、Na2O的问题,本文建立一种偏硼酸锂-四硼酸锂熔融-电感耦合等离子体发射光谱法同时测定石膏中CaO、SO3、Al2O3、Fe2O3、MgO、TiO2、K2O、Na2O、SiO2含量。实验优化了熔剂用量、熔融温度,结果表明采用试样与偏硼酸锂-四硼酸锂混合熔剂质量比例1:5,在铂金坩埚中1000 ℃熔融10 min,在超声条件下,于50 mL 10 %盐酸中浸取熔融物,能够有效分解试样而浸取待测组分。向标准溶液系列中加入偏硼酸锂-四硼酸锂-盐酸基体溶液以消除基体对测试结果的影响。各待测组分的校准曲线的相关性系数均大于0.9990,方法检出限在3~292 μg/g范围内;采用实验方法分别对国家一级标准物质GBW03109a、GBW03110和实际样品进行测定,标准物质的5次平行测试的相对标准偏差在0.14 %~8.86 %之间,测定结果的相对误差在0.03~8.75 %之间,测试结果与标准值无显著性差异;实际样品中各成分测定值的RSD(n=5)为0.24~8.80 %。该方法操作简单、准确度高、精密度好、检出限低,可以同时测定石膏中的多组分含量,能够为石膏资源综合利用调查评价提供一定的技术支撑 。  相似文献   
7.
提出了毛细管固相微萃取-超高效液相色谱-串联质谱法测定血浆中麻醉精神药物含量的方法。取样品1mL,加硼砂缓冲液2mL混匀,离心,上清液转入注射器针管中,接内壁固定有DB-5毛细管色谱柱的不锈钢针头,置于注射泵上以200μL·min-1流量排出样品,用1mL水冲洗针头,再用50μL乙腈洗脱2min。以梯度洗脱-电喷雾正离子源-多反应监测测定洗脱液中药物成分。16种药物的检出限小于10μg·L-1,18种药物的检出限在10~50μg·L-1之间,3种药物的检出限不小于77μg·L-1,5种药物未能检出。血浆中37种药物回收率在4.0%~93.5%之间,相对标准偏差(n=6)在0.80%~13%之间。76起案例样品中检出31例。  相似文献   
8.
马桂秋 《高分子科学》2015,33(5):669-673
This study aims to investigate the chemical structure and morphology of plasmapolymers produced by deposition of ethylene on the surface of polypropylene. The deposition films(sediments) of ethylene plasma on the surface of polypropylene are nonuniform, and the characterization results indicate the existence of hydroxyl groups and aldehyde(or ketone) groups in the sediments. The sediment of ethylene plasma on the polypropylene surface could induce the growth of β-form crystals in the surface layer of polypropylene.  相似文献   
9.
Though it is standard practice to test the stability of analytes in the matrix for routine bioanalytical method, stability evaluation is always impractical and skipped in untargeted lipidomic and metabolomic analysis because analytes in these studies are enormous, diverse and sometimes unknown. Lipidome represents a major class of plasma metabolome and shows great potential to be diagnostic and prognostic biomarkers. However, lipidome also faces stability problems because plasma contains kinds of lipid degradation enzyme. Here, using liquid chromatography time of flight mass spectrometry based lipidomic methodology, plasma levels of various lipids including triglyceride (TG), diglyceride (DG), free fatty acid (FFA), phosphatidylethanolamine (PE) phosphatidylcholine (PC), lyso-phosphatidylcholine (LPC), lyso-phosphatidylethanolamine (LPE), and sphingomyelin (SM) were dynamically determined within 4 h at ambient temperature. In mouse and rat plasma, the levels of most TG, DG, PC and PE species significantly decreased with respect to time, whereas those of LPC, LPE and FFA significantly increased with respect to time. However, such changes did not occur in human plasma, thus indicating hepatic lipase and esterase might involve in the species-specified degradation of lipid classes in plasma. Phenylmethanesulfonyl fluoride (PMSF) pretreatment prevented such lipidome instability in mouse plasma. The results suggested the instability of plasma lipidome should be highly concerned, and the enhancement of ex vivo stability of plasma lipidome could enable more reliable clinical translation of lipidomic data for biomarker discovery.  相似文献   
10.
In this contribution, surface-enhanced Raman spectroscopy (SERS) based on conical holed glass substrates deposited with silver colloids was reported for the first time. It combines the advantages of both dry SERS assays based on plane films deposited with silver colloids and wet SERS assays utilizing cuvettes or capillary tubes. Compared with plane glass substrates deposited with silver colloids, the conical holed glass substrates deposited with silver colloids exhibited five-to ten-folds of increase in the rate of signal enhancement, due to the internal multiple reflections of both the excitation laser beam and the Raman scattering photons within conical holes. The application of conical holed glass substrates could also yield significantly stronger and more reproducible SERS signals than SERS assays utilizing capillary tubes to sample the mixture of silver colloids and the solution of the analyte of interest. The conical holed glass substrates in combination with the multiplicative effects model for surface-enhanced Raman spectroscopy (MEMSERS) achieved quite sensitive and precise quantification of 6-mercaptopurine in complex plasma samples with an average relative prediction error of about 4% and a limit of detection of about 0.02 μM using a portable i-Raman 785H spectrometer. It is reasonable to expect that SERS technique based on conical holed enhancing substrates in combination with MEMSERS model can be developed and extended to other application areas such as drug detection, environmental monitoring, and clinic analysis, etc.  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