全文获取类型
收费全文 | 10780篇 |
免费 | 646篇 |
国内免费 | 441篇 |
专业分类
11867篇 |
出版年
2023年 | 156篇 |
2022年 | 224篇 |
2021年 | 268篇 |
2020年 | 285篇 |
2019年 | 306篇 |
2018年 | 366篇 |
2017年 | 225篇 |
2016年 | 259篇 |
2015年 | 343篇 |
2014年 | 512篇 |
2013年 | 645篇 |
2012年 | 367篇 |
2011年 | 583篇 |
2010年 | 468篇 |
2009年 | 599篇 |
2008年 | 578篇 |
2007年 | 578篇 |
2006年 | 535篇 |
2005年 | 515篇 |
2004年 | 453篇 |
2003年 | 352篇 |
2002年 | 353篇 |
2001年 | 260篇 |
2000年 | 215篇 |
1999年 | 228篇 |
1998年 | 204篇 |
1997年 | 199篇 |
1996年 | 145篇 |
1995年 | 152篇 |
1994年 | 139篇 |
1993年 | 127篇 |
1992年 | 114篇 |
1991年 | 91篇 |
1990年 | 93篇 |
1989年 | 103篇 |
1988年 | 77篇 |
1987年 | 71篇 |
1986年 | 60篇 |
1985年 | 62篇 |
1984年 | 112篇 |
1983年 | 92篇 |
1982年 | 81篇 |
1981年 | 62篇 |
1980年 | 54篇 |
1979年 | 39篇 |
1978年 | 25篇 |
1977年 | 24篇 |
1976年 | 14篇 |
1975年 | 12篇 |
1973年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Ulrich Schulte 《Journal of bioenergetics and biomembranes》2001,33(3):205-212
Proteins specifically involved in the biogenesis of respiratory complex I in eukaryotes have been characterized. The complex I intermediate associated proteins CIA30 and CIA84 are tightly bound to an assembly intermediate of the membrane arm. Like chaperones, they are involved in multiple rounds of membrane arm assembly without being part of the mature structure. Two biosynthetic subunits of eukaryotic complex I have been characterized. The acyl carrier subunit is needed for proper assembly of the peripheral arm as well as the membrane arm of complex I. It may interact with enzymes of a mitochondrial fatty acid synthetase. The 39/40-kDa subunit appears to be an isomerase with a tightly bound NADPH. It is related to a protein family of reductases/isomerases. Both subunits have been discussed to be involved in the synthesis of a postulated, novel, high-potential redox group. 相似文献
72.
Mátrai J Lammens W Jonckheer A Le Roy K Rabijns A Van den Ende W De Maeyer M 《Proteins》2008,71(2):552-564
In the present study, we report on the X-ray crystallographic structure of a GH32 invertase mutant, (i.e., the Arabidopsis thaliana cell-wall invertase 1-E203Q, AtcwINV1-mutant) in complex with sucrose. This structure was solved to reveal the features of sugar binding in the catalytic pocket. However, as demonstrated by the X-ray structure the sugar binding and the catalytic pocket arrangement is significantly altered as compared with what was expected based on previous X-ray structures on GH-J clan enzymes. We performed a series of docking and molecular dynamics simulations on various derivatives of AtcwINV1 to reveal the reasons behind this modified sugar binding. Our results demonstrate that the E203Q mutation introduced into the catalytic pocket triggers conformational changes that alter the wild type substrate binding. In addition, this study also reveals the putative productive sucrose binding modus in the wild type enzyme. 相似文献
73.
Laura ConteBernard L. Trumpower Vincenzo Zara 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2011,1813(1):91-101
The yeast cytochrome bc1 complex, a component of the mitochondrial respiratory chain, is composed of ten distinct protein subunits. In the assembly of the bc1 complex, some ancillary proteins, such as the chaperone Bcs1p, are actively involved. The deletion of the nuclear gene encoding this chaperone caused the arrest of the bc1 assembly and the formation of a functionally inactive bc1 core structure of about 500-kDa. This immature bc1 core structure could represent, on the one hand, a true assembly intermediate or, on the other hand, a degradation product and/or an incorrect product of assembly. The experiments here reported show that the gradual expression of Bcs1p in the yeast strain lacking this protein was progressively able to rescue the bc1 core structure leading to the formation of the functional homodimeric bc1 complex. Following Bcs1p expression, the mature bc1 complex was also progressively converted into two supercomplexes with the cytochrome c oxidase complex. The capability of restoring the bc1 complex and the supercomplexes was also possessed by the mutated yeast R81C Bcsp1. Notably, in the human ortholog BCS1L, the corresponding point mutation (R45C) was instead the cause of a severe bc1 complex deficiency. Differently from the yeast R81C Bcs1p, two other mutated Bcs1p's (K192P and F401I) were unable to recover the bc1 core structure in yeast. This study identifies for the first time a productive assembly intermediate of the yeast bc1 complex and gives new insights into the molecular mechanisms involved in the last steps of bc1 assembly. 相似文献
74.
Diurnal changes in needle gas exchange in alpine Pinus pumila during snow-melting and summer seasons
Atsushi Ishida Takashi Nakano Seikoh Sekikawa Emiko Maruta Takehiro Masuzawa 《Ecological Research》2001,16(1):107-116
Pinus pumila (Pallas) Regel. is a dominant dwarf tree in alpine regions of Japan. The possible factors limiting the net photosynthetic rate (Pn) of the needles of P. pumila were examined in the snow-melting (May) and the summer (August) seasons. In August, in situ maximum Pn was 20 mol kg–1 needle s–1 in the current-year needles and 25 mol kg–1 needle s–1 in the 1-year-old needles. Diurnal trends of Pn in August were positively related to fluctuations in photosynthetic photon flux density (PPFD) and no midday depression of Pn was found, indicating that a decrease in PPFD rather than an increase in needle-to-air vapor pressure deficit (W) might cause the reduction of Pn. Both stomatal conductance (gs) and Pn were lower in May than in August. In May, Pn and gs were almost zero in the morning, but gradually increased with decreasing W, reaching maximum Pn values (4 mol kg–1 needle s–1) and gs (60 mmol kg–1 needle s–1) at 16.00 hours. The daytime Pn in May was positively related to gs. Relative water content in the exposed needles above the snow in May was 83%, which was far above the lethal level. This indicates that the water flow from stems or soils to needles was enough to compensate for a small amount of water loss due to the low gs in May, although the water supplied to needles would be impeded by the low temperatures. Thus, the reduced gs in May would be important for avoiding needle desiccation, and would result in a reduced Pn. 相似文献
75.
Nancy L. Charó Natalia M. Galigniana Graciela Piwien-Pilipuk 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2018,1865(2):432-443
Confocal and electron microscopy images, and WB analysis of cellular fractions revealed that HP1γ is in the nucleus but also in the cytoplasm of C2C12 myoblasts, myotubes, skeletal and cardiac muscles, N2a, HeLa and HEK293T cells. Signal specificity was tested with different antibodies and by HP1γ knockdown. Leptomycin B treatment of myoblasts increased nuclear HP1γ, suggesting that its nuclear export is Crm-1-dependent. HP1γ exhibited a filamentous pattern of staining partially co-localizing with actin in the cytoplasm of myotubes and myofibrils. Immunoelectron microscopic analysis showed high-density immunogold particles that correspond to HP1γ localized to the Z-disk and A-band of the sarcomere of skeletal muscle. HP1γ partially co-localized with actin in C2C12 myotubes and murine myofibrils. Importantly, actin co-immunoprecipitated with HP1γ in the nuclear and cytosolic fractions of myoblasts. Actin co-immunoprecipitated with HP1γ in myoblasts incubated in the absence or presence of the actin depolymerizing agent cytochalasin D, suggesting that HP1γ may interact with G-and F-actin. In the cytoplasm, HP1γ was associated to the perinuclear actin cap that controls nuclear shape and position. In the nucleus, re-ChIP assays showed that HP1γ-actin associates to the promoter and transcribed regions of the house keeping gene GAPDH, suggesting that HP1γ may function as a scaffold protein for the recruitment of actin to control gene expression. When HP1γ was knocked-down, myoblasts were unable to differentiate or originated thin myotubes. In summary, HP1γ is present in the nucleus and the cytoplasm interacting with actin, a protein complex that may exert different functions depending on its subcellular localization. 相似文献
76.
We have investigated the role of polyunsaturated fatty acids in photosynthesis using a triple mutant of Arabidopsis thaliana that lacks trienoic fatty acids (fad 3-2 fad 7-2 fad 8). Though this mutant is male sterile, vegetative growth and development under normal conditions are largely unaffected (McConn
and Browse, 1996 Plant Cell 8: 403–416). At 0.2–1.0 kPa vapor pressure deficit (low VPD), maximum photosynthetic rates of
wild-type and mutant plants were similar while stomatal conductance rates were up to 2 times higher in mutant plants. However,
light-saturated rates of carbon assimilation and stomatal conductance in the mutant were lower than in wild-type plants when
measured at ambient (35 Pa) CO2 and 2.0–2.8 kPa vapor pressure deficit (high VPD). The limitation to photosynthesis in the mutant plants at high VPD was
overcome by saturating partial pressures of CO2 suggesting a stomatal limitation. Chlorophyll fluorescence measurements indicate that differences observed in maximum assimilation
rates were not due to limitations within the photochemical reactions of photosynthesis. Stomatal response to VPD and intrinsic
water use efficiency was drastically different in mutant versus wild-type plants. The results of this investigation indicate
that for Arabidopsis, polyunsaturated fatty acids may be an important determinant of responses of photosynthesis and stomatal conductance to environmental
stresses such as high VPD.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
77.
Georges TawilAnders Viksø-Nielsen Agnès Rolland-SabatéPaul Colonna Alain Buléon 《Carbohydrate polymers》2012,87(1):46-52
A new α-amylase from Anoxybacillus flavothermus (AFA) was found to be effective in hydrolyzing raw starch in production of glucose syrup at temperatures below the starch gelatinization temperature. AFA is very efficient, leading to 77% hydrolysis of a 31% raw starch suspension. The final hydrolysis degree is reached in 2-3 h at starch concentrations lower than 15% and 8-24 h at higher concentrations. AFA is also very efficient in hydrolyzing the crystalline domains in the starch granule. The major A-type crystalline structure is more rapidly degraded than amorphous domains in agreement with the observed preferential hydrolysis of amylopectin. Amylose-lipid complexes are degraded in a second step, yielding amylose fragments which then re-associate into B-type crystalline structures forming the final α-amylase resistant fraction. The mode of action of AFA and the factors limiting complete hydrolysis are discussed in details. 相似文献
78.
André R. Fajardo Laís C. LopesAntonio G.B. Pereira Adley F. RubiraEdvani C. Muniz 《Carbohydrate polymers》2012,87(3):1950-1955
This work reports on the formation and characterization of a polyelectrolyte complex based on pectin (PT), functionalized with primary amine groups (PT-NH2), and chondroitin sulfate (CS). From the simple mixture of PT-NH2 and CS, in acid conditions, it was formed a polyelectrolyte complex, labeled as PT-NH2/CS complex, which was confirmed through FTIR spectroscopy. The electrostatic interactions among the protonated amine groups from PT-NH2 and the sulfate groups from CS are responsible by complex formation. XRD patterns and thermal analysis showed that the complex formation disrupts some interactions present on the PT-NH2 and CS, but on the other hand, others are created. SEM images showed that the PT-NH2/CS complex presents a porous and rough morphology. PT-NH2/CS complex is new material that maintains the properties of CS with synergic association of properties from both polymers, which could maximize its applicability as biomaterial, for example. 相似文献
79.
Shoei Furukawa Isao Kamo Yoshiko Furukawa Saeko Akazawa Eijiro Satoyoshi Koji Itoh Kyozo Hayashi 《Journal of neurochemistry》1983,40(3):734-744
Abstract: A sensitive two-site enzyme immunoassay system for mouse β nerve growth factor (NGF) was developed, based on the sandwiching of the antigen between anti-mouse β NGF antibody IgG coated to a polystyrene tube and anti-mouse β NGF antibody Fab'-linked β- d -galactosidase (β- d -galactoside hydrolase, EC 3.2.1.23). This method has the following advantages: (a) the procedures are simple and rapid compared to bioassay or two-site radioimmunoassay; (b) antibody Fab'-β- d -galactosidase complex is more stable than 125 I-labeled antibody; (c) purified β NGF is detectable at a concentration as low as 10 pg/ml. Our enzyme immunoassay was used to examine the levels of NGF in some tissues of mice. The submaxillary gland contained a high concentration of NGF. However, other tissues, such as the heart, brain, and skeletal muscle, and serum did not contain detectable NGF. These results support recent findings by other investigators that NGF was not found in the organs/tissues other than the submaxillary gland of mice. 相似文献
80.
Somaye Shahraki Fereshteh Shiri Mostafa Heidari Majd Somaye Dahmardeh 《Journal of biomolecular structure & dynamics》2019,37(8):2072-2085
In this study, a new lanthanum (III)-amino acid complex utilizing cysteine has been synthesized and characterized. The anticancer activities of the prepared La(III) complex against MCF-7 cell lines were studied. Results of MTT assay showed that at all three incubation times, the cytotoxic effect of prepared La(III) complex on MCF-7 breast cancer cell lines displays a time- and dose-dependent inhibitory effects. The interactions of the La(III) complex with two whey proteins (bovine serum albumin, BSA, and Bovine β-lactoglobulin, βLG) have been explored by using spectroscopic and molecular dicking methods. The obtained results indicated that La(III) complex strongly quenched the fluorescence of two carrier proteins in static quenching mode and also, BSA hah stronger binding affinity toward studied complex than βLG whit binding constant values of KBSA-La?Complex?~?0.11?×?104 M?1 and KβLG-La?Complex?~?0.63?×?103 M?1 at 300 K. The thermodynamic parameters revealed the contribution of hydrogen bond and Vander Waals interactions in both systems. The distances of the La(III) complex whit whey proteins were calculated using Förster energy transfer theory and proved existence of the energy transfer between two proteins and prepared La(III) complex with a high probability. FT-IR and UV–Vis absorption measurements indicated that the binding of the La(III) to BSA and βLG may induce conformational and micro-environmental changes of the proteins. The docking results indicate that the La(III) complex bind to residues located in the site II of BSA and second site of βLG.
Communicated by Ramaswamy H. Sarma 相似文献