全文获取类型
收费全文 | 96478篇 |
免费 | 493篇 |
国内免费 | 885篇 |
专业分类
97856篇 |
出版年
2022年 | 43篇 |
2021年 | 69篇 |
2020年 | 36篇 |
2019年 | 50篇 |
2018年 | 11905篇 |
2017年 | 10720篇 |
2016年 | 7536篇 |
2015年 | 729篇 |
2014年 | 446篇 |
2013年 | 514篇 |
2012年 | 4427篇 |
2011年 | 13035篇 |
2010年 | 12119篇 |
2009年 | 8343篇 |
2008年 | 10000篇 |
2007年 | 11569篇 |
2006年 | 438篇 |
2005年 | 682篇 |
2004年 | 1153篇 |
2003年 | 1162篇 |
2002年 | 926篇 |
2001年 | 301篇 |
2000年 | 204篇 |
1999年 | 67篇 |
1998年 | 48篇 |
1997年 | 63篇 |
1996年 | 36篇 |
1995年 | 29篇 |
1994年 | 29篇 |
1993年 | 57篇 |
1992年 | 55篇 |
1991年 | 78篇 |
1990年 | 44篇 |
1989年 | 34篇 |
1988年 | 48篇 |
1987年 | 43篇 |
1986年 | 14篇 |
1985年 | 16篇 |
1984年 | 33篇 |
1983年 | 30篇 |
1982年 | 15篇 |
1979年 | 12篇 |
1978年 | 13篇 |
1977年 | 16篇 |
1975年 | 11篇 |
1972年 | 253篇 |
1971年 | 280篇 |
1965年 | 13篇 |
1962年 | 24篇 |
1944年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
991.
Elisa d'Aloisio Anna R Paolacci Arun P Dhanapal Oronzo A Tanzarella Enrico Porceddu Mario Ciaffi 《BMC plant biology》2010,10(1):101
Background
The Protein Disulfide Isomerase (PDI) gene family encodes several PDI and PDI-like proteins containing thioredoxin domains and controlling diversified metabolic functions, including disulfide bond formation and isomerisation during protein folding. Genomic, cDNA and promoter sequences of the three homoeologous wheat genes encoding the "typical" PDI had been cloned and characterized in a previous work. The purpose of present research was the cloning and characterization of the complete set of genes encoding PDI and PDI like proteins in bread wheat (Triticum aestivum cv Chinese Spring) and the comparison of their sequence, structure and expression with homologous genes from other plant species. 相似文献992.
Many methods and tools are available for preprocessing high-throughput RNA sequencing data and detecting differential expression. 相似文献
993.
Xin-wei Wang Ai-sheng Xiong Quan-hong Yao Zhen Zhang Yu-shan Qiao 《Molecular biotechnology》2010,44(1):61-65
Low molecular weight RNA (LMW RNA) is generally obtained either from the total RNA or from total nucleic acids solution. Many
steps and chemical reagents are involved in traditional methods for LMW RNA isolation where degradation of LMW RNA often occurs,
especially for plant materials with high levels of secondary catabolites. In this study, an efficient method was developed
to directly isolate pure LMW RNA from pear peel, a material rich in polyphenolics that is covered with a layer of wax. The
method was based on polyethylene glycol (PEG) precipitation combining CTAB buffer which is often used to isolate RNA from
polysaccharide-rich and polyphenolics-rich materials. The entire procedure could be completed within 6 h and many samples
could be processed at the same time. Few and common chemicals are used with this method. Hence, it could be used as an ordinary
method in the laboratory. The developed method was further tested by isolating LMW RNA from Arabidopsis. Using the isolated LMW RNA samples, microRNAs were successfully detected and characterized. 相似文献
994.
Background
Increased Al concentration causes reduction of mitotic activity, induction of nucleolar alteration, increase of the production of ROS and alteration of several antioxidant enzyme activities in plant cells. Allium cepa is an excellent plant and a useful biomarker for environmental monitoring. Limited information is available about the effects of Al on nucleoli, antioxidant enzyme system, contents of MDA and soluble protein in A. cepa. Therefore, we carried out the investigation in order to better understand the effects of Al on the growth, nucleoli in root tip cells and selected physiological and biochemical characters. 相似文献995.
Ricardo Ribeiro Silva Carlos Renato Corso Dácio Roberto Matheus 《World journal of microbiology & biotechnology》2010,26(5):841-846
Estimating fungal growth is important in processes of soil bioremediation. It has been demonstrated that ergosterol is a good
indicator of fungal biomass in solid substrata. In the present study were evaluated the effects upon the ergosterol rate of
Lentinus crinitus Berk. and Psilocybe castanella Peck through the culture conditions of these fungi, which are evaluated for the bioremediation of soils contaminated by organochlorates.
A good correlation between fungal biomass and ergosterol was observed for both species. The culture conditions did not influence
the ergosterol rate of L. crinitus. Yet the ergosterol rate of P. castanella was influenced from 35 days of culture and when grown in the presence of 15.00 g hexachlorobenzene l−1 of culture medium. So it is possible to estimate growth of both species using ergosterol as indicator in processes of soil
bioremediation since the influences observed in the ergosterol rate of P. castanella are considered. 相似文献
996.
Estimating stand volume in broad-leaved forest using discrete-return LiDAR: plot-based approach 总被引:1,自引:0,他引:1
Keiko Ioki Junichi Imanishi Takeshi Sasaki Yukihiro Morimoto Katsunori Kitada 《Landscape and Ecological Engineering》2010,6(1):29-36
Quantitative assessment of forests is important at a variety of scales for forest planning and management. This study investigated
the use of small-footprint discrete-return lidar for estimating stand volume in broad-leaved forest at plot level. Field measurements
were conducted at 20 sample plots in the study area in western Japan, composed of temperate broad-leaved trees. Five height
variables and two density variables were derived from the lidar data: 25th, 50th, 75th, and 100th percentiles, and mean of
laser canopy heights as height variables (h
25, h
50, h
75, h
100, h
mean); and ground fraction and only-and-vegetation fraction (d
GF, d
OVF) as density variables, defined respectively as the proportion of laser returns that reached the ground, and the proportion
of only echoes (i.e., single pulse returns for which the first and last pulses returned from the same point) within vegetation
points. In addition, the normalized difference vegetation index (NDVI), which is often used as an estimator for leaf area
index (LAI) and above-ground biomass, was derived from multispectral digital imagery as an alternative density variable (d
NDVI). Nonlinear least-square regression with cross-validation analysis was performed with single variables and combinations;
a total of 23 models were studied. The best prediction was found when h
75 and d
OVF were used as independent variables, resulting in adjusted R
2 of 0.755 and root-mean-square error (RMSE) of 41.90 m3 ha−1, corresponding to 16.4% of the mean stand volume, better than or comparable to the prediction models of previous studies. 相似文献
997.
Shari L. Laprise 《Molecular biotechnology》2010,45(2):187-197
The “holy grail” of regenerative medicine is the identification of an undifferentiated progenitor cell that is pluripotent,
patient specific, and ethically unambiguous. Such a progenitor cell must also be able to differentiate into functional, transplantable
tissue, while avoiding the risks of immune rejection. With reports detailing aberrant genomic imprinting associated with assisted
reproductive technologies (ART) and reproductive cloning, the idea that human embryonic stem cells (hESCs) derived from surplus
in vitro fertilized embryos or nuclear transfer ESCs (ntESCs) harvested from cloned embryos may harbor dangerous epigenetic
errors has gained attention. Various progenitor cell sources have been proposed for human therapy, from hESCs to ntESCs, and
from adult stem cells to induced pluripotent stem cells (iPS and piPS cells). This review highlights the advantages and disadvantages
of each of these technologies, with particular emphasis on epigenetic stability. 相似文献
998.
There is a special emphasis today on integrating traditional healing within health services. However, most areas in which
there is a system of traditional healing have undergone colonization and a number of pressures suppressing tradition for hundreds
of years. The question arises as to how one can understand today’s tradition in light of earlier traditions. This article
is based on material collected in Sámi areas of Finnmark and Nord-Troms Norway; it compares local healing traditions with
what is known of earlier shamanic traditions in the area. The study is based on 27 interviews among healers and their patients.
The findings suggest that although local healing traditions among the Sámi in northern Norway have undergone major transformations
during the last several hundred years, they may be considered an extension of a long-standing tradition with deep roots in
the region. Of special interest are also the new forms tradition may take in today’s changing global society. 相似文献
999.
K Königsson K Törneke IV Engeland K Odensvik H Kindahl 《Acta veterinaria Scandinavica》2003,44(4):153
The pharmacokinetics and the prostaglandin (PG) synthesis inhibiting effect of flunixin were determined in 6 Norwegian dairy
goats. The dose was 2.2 mg/kg body weight administered by intravenous (i.v.), intramuscular (i.m.) and oral (p.o.) routes
using a cross-over design. Plasma flunixin content was analysed by use of liquid chromatography and the PG synthesis was evaluated
by measuring plasma 15-ketodihydro-PGF2α by a radioimmuno-assay. Results are presented as median (range). The elimination half-lives (t1/2·λ) were 3.6 (2.0–5.0), 3.4 (2.6–6.8) and 4.3 (3.4–6.1) h for i.v., i.m. and p.o. administration, respectively. Volume of distribution
at steady state (Vdss) was 0.35 (0.23–0.41) L/kg and clearance (CL), 110 (60–160) mL/h/kg. The plasma concentrations after oral administration
showed a double-peak phenomenon with the two peaks occurring at 0.37 (0.25–1) and 3.5 (2.5–5.0) h, respectively. Both peaks
were in the same order of magnitude. Bioavailability was 79 (53–112) and 58 (35%–120)% for i.m. and p.o. administration, respectively.
15-Ketodihydro-PGF2α plasma concentrations decreased after flunixin administration independent of the route of administration. 相似文献
1000.
Subspecific relationships of the European beaverCastor fiber have been obscured by failure to follow the rules of the International Code of Zoological Nomenclature and remain an open
issue. Inconsequence in the use of subspecies names caused a nomenclatural as well as a taxonomic confusion. We discuss these
controversial and incorrect nomenclatural decisions, and recognize 9 nominal subspecies of European beaver, bearing 9 available
names:C. f. fiber Linnaeus, 1758,C. f. galliae Geoffroy, 1803, C. f. albicus Matschie, 1907,C. f. vistulanus Matschie, 1907,C. f. pohlei Serebrennikov, 1929,C. f. birulai Serebrennikov, 1929,C. f. tuvinicus Lavrov, 1969,C. f. belorussicus Lavrov, 1981, andC. f. orientoeuropaeus Lavrov, 1981. 相似文献