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971.
以半纤维素主要成分木聚糖的两种单体--吡喃木糖和O-乙酰基吡喃木糖为模型化合物,运用密度泛函理论(DFT),采用B3LYP方法和6-31+G(d,p)基组进行计算,研究了吡喃木糖热解形成HAA的6条可能的反应路径和O-乙酰基吡喃木糖热解形成HAA的3条可能的反应路径。由此确定了吡喃木糖热解形成HAA的最优路径为:吡喃木糖首先开环得到链式木糖,然后C3羟基和C2氢脱水,随后经重排和逆醇醛缩合反应生成包含C4/C5的HAA;该路径的决速步骤为脱水反应,能垒为253.3 kJ/mol。O-乙酰基吡喃木糖热解形成HAA的最优路径为:O-乙酰基吡喃木糖首先支链断裂脱出乙酸(AA),开环后的链式中间体经氢转移反应得到包含C4/C5的HAA;该路径的决速步骤为最后的氢转移反应,能垒为317.6 kJ/mol。 相似文献
972.
Ru添加对Co/SiO费托合成催化剂性能的影响 《燃料化学学报》2015,43(10):1230-1238
用初湿含浸法制备了不同Ru添加量的Co/SiO2模型催化剂,然后进行N2物理吸附、XRD、H2-TPD、DRIFTS等表征和微分固定床费托(F-T)反应评价。F-T反应结果表明,催化剂中添加Ru后,CO转化率显著提高,TOF值增大,CO2和CH4选择性降低,烯/烷比(O/P)降低。FT-IR表征说明,催化剂添加Ru后Co-O键的强度减弱,相对应的H2-TPR也表明,催化剂的还原度得到显著提高。还原后的催化剂XRD结果进一步证实,加入Ru后,催化剂无钴氧化物被检出,并且当Ru添加量为0.5%(质量分数)时催化剂中金属钴主要以六方密堆(hcp)形式存在。CO-DRIFTS结果显示,Ru的加入使CO的吸收峰发生红移,即Ru促进了CO的解离。H2-TPD结果则表明,随着Ru添加量的增加,催化剂表面COads/Cos和CO*/Cos增大,这是CH4选择性降低的主要原因。 相似文献
973.
预裂化理论研究:基质表面酸性位类型及不同类型酸性位接触顺序对裂化过程小分子烯烃收率的影响 《燃料化学学报》2015,43(11):1350-1358
在区分氢负离子转移反应与氢转移反应、非选择性氢转移反应与总的氢转移反应的情况下,通过合成物性相近但酸性不同的氧化铝,用以作为裂化催化剂基质材料,在固定床反应器上考察了催化裂化过程,基质酸性位类型及基质表面Lewis及Brönsted酸性位接触顺序对小分子烯烃(丙烯、丁烯)收率的影响。结果表明,催化裂化生成小分子烯烃过程中,分子筛与基质所呈现出的反应特点存在较大的区别,前者活性虽高,但总的氢转移反应活性过强。基质材料裂化活性虽低但其表面以氢负离子转移反应为主,反应路径角度更有利于小分子烯烃收率的提高。另外,基质表面存在Brönsted酸性位,或原料油首先与基质表面Lewis酸性位相接触再与Brönsted酸性位反应的预裂化过程,会在促进裂化反应发生的同时抑制总的氢转移反应,更有利于小分子烯烃收率的提高。 相似文献
974.
Haiying Yang Zhejian Li Meng Shan Congcong Li Honglan Qi Qiang Gao Jinyi Wang Chengxiao Zhang 《Analytica chimica acta》2015
A highly selective and sensitive electrogenerated chemiluminescence (ECL) biosensor for the detection of prostate PC-3 cancer cells was designed using a prostate specific antibody as a capture probe and ruthenium complex-labelled wheat germ agglutinin as a signal probe. The ECL biosensor was fabricated by covalently immobilising the capture probe on a graphene oxide-coated glassy carbon electrode. Target PC-3 cells were selectively captured on the surface of the biosensor, and then, the signal probe was bound with the captured PC-3 cells to form a sandwich. In the presence of tripropylamine, the ECL intensity of the sandwich biosensor was logarithmically directly proportion to the concentration of PC-3 cells over a range from 7.0 × 102 to 3.0 × 104 cells mL−1, with a detection limit of 2.6 × 102 cells mL−1. The ECL biosensor was also applied to detect prostate specific antigen with a detection limit of 0.1 ng mL−1. The high selectivity of the biosensor was demonstrated in comparison with that of a lectin-based biosensor. The strategy developed in this study may be a promising approach and could be extended to the design of ECL biosensors for highly sensitive and selective detection of other cancer-related cells or cancer biomarkers using different probes. 相似文献
975.
Paecilomycines A and B,Novel Diterpenoids,Isolated from Insect‐Pathogenic Fungi Paecilomyces sp. ACCC 37762
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Kun Zhou Xiao‐Ling Zhao Li‐Ping Han Meng‐Meng Cao Chuan Chen Bao‐Zhong Shi Du‐Qiang Luo 《Helvetica chimica acta》2015,98(5):642-649
Two new diterpenoids, named paecilomycine A ( 1 ) and paecilomycine B ( 2 ), including a novel skeleton with a five‐membered lactone ring, together with three known labdane diterpenoids, rel‐(1R,3S,4aS,5R,8aS)‐5‐[(3E)‐4‐carboxy‐3‐methylbut‐3‐en‐1‐yl]decahydro‐3‐hydroxy‐1,4a‐dimethyl‐6‐methylidenenaphthalene‐1‐carboxylic acid ( 3 ), botryosphaerin E ( 4 ), and agathic acid ( 5 ), were isolated from solid culture of the insect pathogenic fungi strain Paecilomyces sp. The structures of all compounds were established on the basis of comprehensive spectroscopic studies. The relative configurations of 1 and 2 were determined by single‐crystal X‐ray diffraction analyses. 相似文献
976.
977.
978.
979.
Stochastic/Controlled Symmetry Breaking of the T8‐POSS Cages toward Multifunctional Regioisomeric Nanobuilding Blocks
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Xiao‐Man Wang Qing‐Yun Guo Shuai‐Yuan Han Jing‐Yi Wang Di Han Prof. Qiang Fu Prof. Wen‐Bin Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(43):15246-15255
Precise synthesis of nanobuilding blocks with accurately positioned functional groups presents a daunting challenge. Herein, a practical synthesis and thorough characterization of a series of T8‐polyhedral oligomeric silsesquioxane (POSS) di‐ and triadducts is reported. Upon addition of triflic acid across the double bonds in octavinylPOSS (V8T8) followed by hydrolysis, the cubic symmetry of the T8‐POSS cage (Oh) is broken into C2v (ortho‐), C2v (meta‐), and D3d (para‐) for diadducts and further to Cs (oom‐), Cs (omp‐), and C3v (mmm‐) for triadducts in a stochastic fashion. Their structures and regioconfigurations have been unambiguously demonstrated by 1H, 13C, and 29Si NMR spectroscopy, as well as MALDI‐TOF mass spectrometry. The assignment of the diadducts was further corroborated by converting each individual diadduct into triadduct(s), the structure of which is controlled by the symmetry of the precursor. Except for the C3v triadduct, they can all be prepared in synthetically useful quantities. The presence of two types of highly reactive and mutually orthogonal functional groups facilitates further modification into complex nanostructures and composite materials. These unique regioisomers provide a versatile platform for constructing giant molecules and Janus silsesquioxanes. 相似文献
980.
Catalytic Asymmetric Construction of α‐Quaternary Cyclopentanones and Its Application to the Syntheses of (−)‐1,14‐Herbertenediol and (−)‐Aphanorphine
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Dao‐Yong Zhu Ming‐Hui Xu Prof. Dr. Yong‐Qiang Tu Prof. Dr. Fu‐Min Zhang Prof. Dr. Shao‐Hua Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(44):15502-15505
A novel and efficient strategy to build α‐benzylic quaternary cyclopentanones with excellent enantioselectivities (up to 96 % ee) and high yields (up to 99 % yield) has been developed, and its application demonstrated by the first catalytic asymmetric total synthesis of (?)‐1,14‐herbertenediol and the formal synthesis of (?)‐aphanorphine. 相似文献