全文获取类型
收费全文 | 1956篇 |
免费 | 102篇 |
出版年
2023年 | 10篇 |
2022年 | 10篇 |
2021年 | 32篇 |
2020年 | 21篇 |
2019年 | 36篇 |
2018年 | 55篇 |
2017年 | 59篇 |
2016年 | 67篇 |
2015年 | 103篇 |
2014年 | 97篇 |
2013年 | 149篇 |
2012年 | 163篇 |
2011年 | 151篇 |
2010年 | 103篇 |
2009年 | 74篇 |
2008年 | 132篇 |
2007年 | 134篇 |
2006年 | 110篇 |
2005年 | 121篇 |
2004年 | 110篇 |
2003年 | 114篇 |
2002年 | 74篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 6篇 |
1998年 | 19篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 11篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1975年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2058条查询结果,搜索用时 31 毫秒
111.
Bryl K 《Cellular & molecular biology letters》2003,8(2):285-296
Rhodopsins are currently known to belong to two distinct protein families. The visual rhodopsins, found in eyes throughout the animal kingdom, are photosensory pigments. Archaeal rhodopsins, found in extreme halophiles, function as light-driven proton pumps (bacteriorhodopsins), chloride ion pumps (halorhodopsins), or photosensory receptors (sensory rhodopsins). Light absorption by rhodopsins triggers their characteristic photoconversion extending into the (milli)second time range. There are three main paradigms of rhodopsins photoconversion. (1) Initiation of the trans-cis isomerization is the very primary consequence of light absorption. (2) Rhodopsins store light energy via the charge-separation mechanism (the charge of Schiff base is separated from its counterion). (3) Full trans-cis isomerization of the chromophore is a prerequisite for the full biological activity of rhodopsins. These paradigms will be questioned. 相似文献
112.
Okon K Szumera A Papla B Pietkun I Zdunczyk A Rucinska M Skotnicki AB Stachura J 《Analytical and quantitative cytology and histology / the International Academy of Cytology [and] American Society of Cytology》2003,25(4):227-234
OBJECTIVE: To analyze cytologic and histologic parameters in bone marrow trephine biopsy in an attempt to define heterogeneity of hairy cell leukemia cells. STUDY DESIGN: The study group consisted of 28 trephine biopsies. Immunohistochemistry for CD20 antigen was used. Image processing and measurements were performed with AnalySIS 3.0 image analysis system (Soft Imaging System GmbH, Germany) and custom built programs. For planimetric measurements of nuclei, automatic segmentation was implemented. The measured parameters were: surface area, perimeter, minimum, mean and maximum diameter, and a set of form factors. Relative volumes of bone trabeculae, adipose tissue, hematopoietic tissue and neoplastic infiltrate were assessed by the point counting method. Nuclear volume was measured by the point sampled intercept method. Bone marrow fibrosis was assessed using a curvilinear line test system. RESULTS: Significant variability of cell nuclei was found, and their classification into 3 types was possible. The relative frequency of those types was different in various cases and allowed subdivision of cases into 3 groups that differed in some clinical and histologic manifestations. CONCLUSION: The present study demonstrated the heterogeneity of cell populations of hairy cell leukemia. 相似文献
113.
It is known that the level of cGMP is modulated in response to a number of stimuli in plant cells but intracellular events distal to cGMP metabolism are not clear. Cyclic GMP-dependent protein kinase (Pk-G) is a major effector of cGMP action in animals and yeasts. We wanted to determine whether such kinase is present in plant cells. A soluble protein kinase was isolated from seedlings of Pharbitis nil and purified following purification methods including anion-exchange and affinity-chromatography. The enzyme consists of a single polypeptide of M(r) 70 kDa as determined by SDS-PAGE. From conventional modulators only cyclic GMP, when applied in low concentration, was able to accelerate the enzyme activity in the presence of histones. The enzyme autophosphorylated on serine and threonine residues and phosphorylated some substrates only on serine residues. Mixture of histones and histones H2B, H3 were the best phosphate acceptors. The process of autophosphorylation was accelerated by a low concentration of cGMP and reduced by high concentration of this second messenger. Antibodies raised against catalytic domain of animals Pk-G I alpha and beta cross-reacted with protein kinase from Pharbitis nil tissue. These data, taken together, demonstrate the presence of functional enzyme, which activity is regulated by cGMP and allow to classify this protein kinase as a member of the second messenger regulated group of enzymes. 相似文献
114.
Arsenic content was assayed in the samples of the femur head of the people living in southern and central Poland (Kraków,
n=13; Silesian region, n=13; Łódź, n=12). The average age being 68.7±8.7 yr. Arsenic content in the femur head was determined applying the hydride generation
atomic absorption spectrometry (HG-AAS) method after microwave mineralization. The average arsenic contents in the femur head
of the residents of the Łódź, Kraków, and Silesian regions were 0.41 μg/g, 0.37 μg/g, and 0.18 μg/g, respectively. No correlation
has been found between arsenic content in the femur head and the content of other metals. Neither the age nor sex of the people
tested affected the arsenic content in the femur head. 相似文献
115.
The objective of this study was to assess the LIF (leukemia inhibitory factor) concentration in uterine flushing and serum (ELISA) of women with proven fertility, infertile women and women with recurrent miscarriage. In addition, progesterone level was determined in serum. A decreased production of LIF in the uterine microenvironment was found in states of impaired fertility. With a cut-off point of 8.23 pg/ml for LIF level in uterine flushings we have achieved 86.7% sensitivity and 100% specificity in detection of women with idiopathic infertility compared to fertile controls. No correlation between LIF in serum and uterine flushing was demonstrated, rendering LIF measurements in serum useless for diagnosis of impaired infertility. We conclude that LIF measurement in uterine flushing could be a useful diagnostic tool to predict unsuccessful implantation. 相似文献
116.
The adsorption isotherm data of (R)- and (S)-1-indanol and of their racemic mixture on cellulose tribenzoate were measured by frontal analysis. The experimental data for each enantiomers were fitted to the single-component bilangmuir isotherm model. The competitive experimental data were fitted to the ideal adsorption solution model (IAS), the real adsorption solution model (RAS), and the bilangmuir thermodynamically consistent model (BTC). The mass transfer kinetic parameters were estimated from systematic comparisons between the experimental single-component band profiles and profiles calculated using the general rate model (GR) of chromatography coupled with the generalized Maxwell-Stefan equation (GMS). The validation of the isotherm model and of the mass transfer kinetic model was made by comparing the experimental band profiles obtained for solutions of the two enantiomers and those calculated with the competitive GR-GMS model. The excellent agreement observed proves that a combination of the BTC isotherm model and the GMS kinetic model, using the best values of the BTC and GMS parameters estimated from single component experiments, allows an excellent prediction of the binary isotherm and the binary mass transfer kinetics. 相似文献
117.
Krawczyk B Naumiuk L Lewandowski K Baraniak A Gniadkowski M Samet A Kur J 《FEMS immunology and medical microbiology》2003,38(3):241-248
Amplification of DNA fragments surrounding rare restriction sites (ADSRRS-fingerprinting) is a novel assay based on suppression of polymerase chain reaction (PCR). This phenomenon allows the amplification of only a limited subset of DNA fragments, since only those with two different oligonucleotides ligated at the ends of complementary DNA strands are amplified in the PCR. The DNA fragments can be easily analyzed on polyacrylamide gels, stained with ethidium bromide. We have implemented this method using a set of clinical Serratia marcescens isolates from three outbreaks ongoing in the Public Hospital in Gdańsk (Poland). Clustering of ADSRRS-fingerprinting data matched epidemiological, microbiological, random amplification of polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE) data. Based on this study, we found that there is at least a similar power of discrimination between the present 'gold-standard' PFGE and the novel method, ADSRRS-fingerprinting. Although the ADSRRS-fingerprinting method may appear to be more complex than the RAPD technique, we found it fast and reproducible. 相似文献
118.
Karasek M Stankiewicz A Bandurska-Stankiewicz E Zylinska K Pawlikowski M Kuzdak K 《Neuro endocrinology letters》2000,21(6):437-439
OBJECTIVES: Surgical removal of a very large goiter may traumatize adjacent anatomical structures. The manipulations that involve superior cervical ganglia may alter melatonin secretion. To test this hypothesis we decided to study diurnal serum melatonin profiles in patients with a very large goiter before and after the surgery. MATERIAL AND METHODS:The study was performed on 10 women (mean age-46.5+/-1.6 years; mean+/-SEM; range 39-54 years) with very large non-toxic nodular goiter (mean thyroid volume-125.8+/-25.9 cm (3); mean+/-SEM; range 82.6-326.7 cm(3)). Diurnal serum melatonin profiles were estimated two days before the operation and 10 days after the surgery. Blood samples were collected at 08:00, 12:00, 16:00, 20:00, 22:00, 24:00, 02:00, 04:00, 06:00 and 08:00 h. Melatonin concentration was measured using RIA kit. RESULTS: Nocturnal serum melatonin concentrations (at 24, 02, and 04 hours) were significantly higher after the surgery than before the operation. CONCLUSIONS: Very large goiter may compress the superior cervical ganglia altering indirectly the melatonin synthesis. It cannot be excluded, however, that the presence of the large goiter in some other way affects melatonin secretion. 相似文献
119.
Structure and function of S-adenosylhomocysteine hydrolase 总被引:6,自引:0,他引:6
Turner MA Yang X Yin D Kuczera K Borchardt RT Howell PL 《Cell biochemistry and biophysics》2000,33(2):101-125
In mammals, S-adenosylhomocysteine hydrolase (AdoHcyase) is the only known enzyme to catalyze the breakdown of S-adenosylhomocysteine
(AdoHcy) to homocysteine and adenosine. AdoHcy is the product of all adenosylmethionine (AdoMet)-dependent biological transmethylations.
These reactions have a wide range of products, and are common in all facets of biometabolism. As a product inhibitor, elevated
levels of AdoHcy suppress AdoMet-dependent transmethylations. Thus, AdoHcyase is a regulator of biological transmethylation
in general. The three-dimensional structure of AdoHcyase complexed with reduced nicotinamide adenine dinucleotide phosphate
(NADH) and the inhibitor (1′R, 2′S, 3′R)-9-(2′,3′-dihyroxycyclopenten-1-yl)adenine (DHCeA) was solved by a combination of
the crystallographic direct methods program, SnB, to determine the selenium atom substructure and by treating the multiwavelength anomalous diffraction data as a special
case of multiple isomorphous replacement. The enzyme architecture resembles that observed for NAD-dependent dehydrogenases,
with the catalytic domain and the cofactor binding domain each containing a modified Rossmann fold. The two domains form a
deep active site cleft containing the cofactor and bound inhibitor molecule. A comparison of the inhibitor complex of the
human enzyme and the structure of the rat enzyme, solved without inhibitor, suggests that a 17° rigid body movement of the
catalytic domain occurs upon inhibitor/substrate binding. 相似文献
120.