全文获取类型
收费全文 | 2181篇 |
免费 | 164篇 |
国内免费 | 16篇 |
出版年
2023年 | 18篇 |
2022年 | 24篇 |
2021年 | 67篇 |
2020年 | 42篇 |
2019年 | 58篇 |
2018年 | 95篇 |
2017年 | 79篇 |
2016年 | 125篇 |
2015年 | 128篇 |
2014年 | 125篇 |
2013年 | 168篇 |
2012年 | 170篇 |
2011年 | 156篇 |
2010年 | 111篇 |
2009年 | 84篇 |
2008年 | 79篇 |
2007年 | 79篇 |
2006年 | 72篇 |
2005年 | 74篇 |
2004年 | 56篇 |
2003年 | 69篇 |
2002年 | 40篇 |
2001年 | 41篇 |
2000年 | 46篇 |
1999年 | 32篇 |
1998年 | 18篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 9篇 |
1993年 | 15篇 |
1992年 | 23篇 |
1991年 | 21篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 17篇 |
1987年 | 20篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1976年 | 7篇 |
1974年 | 5篇 |
1972年 | 12篇 |
1970年 | 5篇 |
1968年 | 6篇 |
1967年 | 9篇 |
1965年 | 7篇 |
排序方式: 共有2361条查询结果,搜索用时 15 毫秒
1.
El-Hadi Ibrahim Adil Denizli Sema Bekta
mer Gen Erhan Pi
kin 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1998,720(1-2):217-224
Poly(2-hydroxyethylmethacrylate–ethyleneglycoldimethacrylate) [poly(HEMA–EGDMA)] microspheres carrying Cibacron Blue F3GA and/or thionein were prepared and used for the removal of cadmium ions Cd(II) from human plasma. The poly(HEMA–EGDMA) microspheres, in the size range of 150–200 μm in diameter, were produced by a modified suspension copolymerization of HEMA and EGDMA. The reactive triazinyl dye-ligand Cibacron Blue F3GA was then covalently incorporated into the microspheres. The maximum dye incorporation was 16.5 μmol/g. Then, thionein was bound onto the Cibacron Blue F3GA-incorporated microspheres under different conditions. The maximum amount of thionein bound was 14.3 mg/g. The maximum amounts of Cd(II) ions removed from human plasma by poly(HEMA–EGDMA)–Cibacron Blue F3GA and poly(HEMA–EGDMA)–Cibacron Blue F3GA–thionein were of 17.5 mg/g and 38.0 mg/g, respectively. Cd(II) ions could be repeatedly adsorbed and desorbed with both types of microspheres without significant loss in their adsorption capacity. 相似文献
2.
L.E. Palma-Cano H.A. Piñon-Castillo S.H. Tarango-Rivero A. Carbon J. Salas-Leiva L.N. Muñoz-Castellanos C. Cravo-Laureau R. Duran E. Orrantia-Borunda 《Letters in applied microbiology》2021,72(5):556-569
We described the bacterial diversity of walnut grove soils under organic and conventional farming. The bacterial communities of rhizospheric and nonrhizospheric soils of pecan tree (Carya illinoensis K. Koch) were compared considering two phenological stages (sprouting and ripening). Sixteen operational taxonomic units (OTUs) were identified significantly more abundant according to the plant development, only one according to the farming condition, and none according to the soil origin. The OTUs specificaly abundant according to plant development included Actinobateria (2) and Betaproteobacteria (1) related OTUs more abundant at the sprouting stage, while at the fruit ripening (FR) stage the more abundant OTUs were related to Actinobacteria (6), Alphaproteobacteria (6), and unclassified Bacteria (1). The Gaiellaceae OTU18 (Actinobacteria) was more abundant under conventional farming. Thus, our study revealed that the plant development stage was the main factor shaping the bacterial community structure, while less influence was noticed for the farming condition. The bacterial communities exhibited specific metabolic capacities, a large range of carbon sources being used at the FR stage. The identified OTUs specifically more abundant represent indicators providing useful information on soil condition, potential tools for the management of soil bacterial communities. 相似文献
3.
4.
D. Lewczuk A. Bereznowski M. Hecold M. Frąszczak A. Ruść A. Korwin-Kossakowska J. Szyda S. Kamiński 《Journal of applied genetics》2018,59(2):225-230
Horses lose potential opportunities because of health problems. Available breeding strategies are not effective enough, probably also because of the different definition used and its genetic usefulness. The aim of the study was to compare the genetic background estimated by the genome-wide association study (GWAS) for osteochondrosis using two different scaling osteochondrosis (OC)/healthy and osteochondrosis dissecans (OCD)/healthy systems for evaluating the disease status of investigated fetlock joints. Two hundred one Warmblood horses trained for performance tests (87 stallions and 114 mares) were phenotyped and genotyped. Four fetlock x-ray images per horse were collected using the RTG Girth HF 80 and Vet Scan ray 3600. The DNA of each horse was genotyped using the BeadChip 70K. To identify SNPs that significantly affect the probability of osteochondrosis, two different methods were applied: the Cochran-Armitage test based on an additive mode of inheritance and logistic regression. The genetic background for osteochondrosis, expressed in the number of SNPs found with significant associations with osteochondrosis, was higher by evaluation in the scale of OCD/healthy horses (16 SNPs on several chromosomes mainly on the ECA1 and ECA10) than OC/healthy (2 SNPs on the ECA15 and one SNP on the ECA10). Detailed definition of osteochondrosis is needed in breeding and in veterinary practice. The genetic background for osteochondrosis and osteochondrosis dissecans seems not the same. Suggestive SNPs could be the candidate markers for osteochondrosis but should be checked on a larger population before usage. 相似文献
5.
6.
Conformational energies for the N-acetyl-N'-methylamides of the 20 natural amino acids were calculated, including the solvent effects, as functions of the angles phi and psi for rotation of the main chain and for six positions chi 1 of the C alpha-C beta bond in the side chain (fixed values for chi 2, chi 3, ...). The computed energies were used to evaluate the mean-square end-to-end distance and mean-square dipole moment of homopolypeptides of the 20 natural amino acids. Ten proteins and three enzymes of current interest were also studied. Slight differences in both properties are found on taking the effects of solvent into consideration. Comparison with other computational and experimental results is made. 相似文献
7.
Comparative studies on the degradation of guanidino and ureido compounds by Pseudomonas 总被引:1,自引:0,他引:1
The utilization of guanidino and ureido compounds was studied in several Pseudomonas species. Multiple routes of agmatine catabolism were found. All members of the homology group I of Pseudomonas use the initial deamination of agmatine to carbamoylputrescine which is subsequently converted to putrescine. In Pseudomonas indigofera, the catabolism of agmatine can also occur via an initial hydrolysis of the amidino group to putrescine catalyzed by an agmatine amidinohydrolase. A third pathway was found in Pseudomonas cepacia, namely oxidative deamination producing guanidinobutyraldehyde catalyzed by agmatine dehydrogenase, followed by formation of guanidinobutyrate and removal of urea by guanidinobutyrate amidinohydrolase to produce 4-aminobutyrate. Novel amidino-hydrolases were characterized in P. putida for the utilization of arcaine and audouine, and in P. cepacia for arcaine, homoarginine and guanidinovalerate. Guanidinovalerate amidinohydrolase was also detected in P. doudoroffii. Some of these amidinohydrolases accept more than one substrate, e.g., guanidinobutyrate and guanidinovalerate utilization by P. doudoroffii and P. cepacia, the catabolism of arcaine and audouine by P. putida, and the degradation of arcaine and homoarginine by P. cepacia. 相似文献
8.
Joanna Nakonieczna Ewelina Michta Magda Rybicka Mariusz Grinholc Anna Gwizdek-Wiśniewska Krzysztof P Bielawski 《BMC microbiology》2010,10(1):323
Background
Staphylococcus aureus, a major human pathogen causes a wide range of disease syndromes. The most dangerous are methicillin-resistant S. aureus (MRSA) strains, resistant not only to all β-lactam antibiotics but also to other antimicrobials. An alarming increase in antibiotic resistance spreading among pathogenic bacteria inclines to search for alternative therapeutic options, for which resistance can not be developed easily. Among others, photodynamic inactivation (PDI) of S. aureus is a promising option. Photodynamic inactivation is based on a concept that a non toxic chemical, called a photosensitizer upon excitation with light of an appropriate wavelength is activated. As a consequence singlet oxygen and other reactive oxygen species (e.g. superoxide anion) are produced, which are responsible for the cytotoxic effect towards bacterial cells. As strain-dependence in photodynamic inactivation of S. aureus was observed, determination of the molecular marker(s) underlying the mechanism of the bacterial response to PDI treatment would be of great clinical importance. We examined the role of superoxide dismutases (Sod) in photodynamic inactivation of S. aureus as enzymes responsible for oxidative stress resistance. 相似文献9.
Neuronal nuclei have a low H1 content. A stoichiometry of 0.47 molecule/nucleosome, on average, is calculated for rat brain cortical neurons by comparing its H1 content with that of liver nuclei. The H1 fraction of rat cerebral cortex neurons has been resolved into five subtypes, H1a--e, that have the same mobility as the unphosphorylated H1 forms of other rat tissues. The subtypes H1a--d decay exponentially during postnatal development and are substituted to different extents by H1e. The higher replacement rate is shown by H1a with an apparent half-lifetime of about 5 days. The corresponding values for H1b, H1c and H1d are 11, 21 and 15 days. Several conclusions can be drawn from the observation of postnatal changes in H1 subtype proportions. The low H1 content of neuronal nuclei does not imply the presence of notable peculiarities in subtype composition or in subtype substitution pattern. There is turnover of H1 in differentiating neurons once cell proliferation and DNA replication have ceased. The relative rates of synthesis and/or degradation of the subtypes differ in germinal cells and in neurons. Comparison with previous results on H1 degrees accumulation also shows that in cortical neurons the regulation of the subtypes H1a--e differs from that of H1 degrees. 相似文献
10.
In recent years the existence of a DNA-repair process in G2 has been proposed to explain the potentiating effects of DNA-repair inhibitors given in G2 on chromatid aberrations (CA) induced by S-dependent as well as S-independent DNA-damaging agents. In the present report, root-tip cells of Allium cepa were exposed to maleic hydrazide (MH) or mitomycin C (MMC) and post-treated in G2 with caffeine (Caff) and various inhibitors of DNA synthesis. No enhancement of chromosome damage was observed when Caff was present in G2, but hydroxyurea (HU) or 5-fluorodeoxyuridine (FdUrd) potentiated the frequencies of CA. A slight additional increase of CA frequencies was observed following treatment with Ara C and excess thymidine in G2. When MH-damaged cells were pulse-treated with Caff earlier during recovery, the yield of CA was enhanced. The earlier Caff was present following MH treatment, the stronger was the potentiation. 相似文献