全文获取类型
收费全文 | 3594篇 |
免费 | 352篇 |
国内免费 | 257篇 |
出版年
2024年 | 4篇 |
2023年 | 33篇 |
2022年 | 91篇 |
2021年 | 162篇 |
2020年 | 128篇 |
2019年 | 145篇 |
2018年 | 150篇 |
2017年 | 108篇 |
2016年 | 150篇 |
2015年 | 231篇 |
2014年 | 269篇 |
2013年 | 256篇 |
2012年 | 356篇 |
2011年 | 276篇 |
2010年 | 180篇 |
2009年 | 142篇 |
2008年 | 163篇 |
2007年 | 166篇 |
2006年 | 146篇 |
2005年 | 136篇 |
2004年 | 118篇 |
2003年 | 125篇 |
2002年 | 131篇 |
2001年 | 95篇 |
2000年 | 84篇 |
1999年 | 74篇 |
1998年 | 38篇 |
1997年 | 34篇 |
1996年 | 27篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 18篇 |
1992年 | 22篇 |
1991年 | 25篇 |
1990年 | 15篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1976年 | 3篇 |
1975年 | 1篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1969年 | 1篇 |
1956年 | 1篇 |
1952年 | 2篇 |
排序方式: 共有4203条查询结果,搜索用时 281 毫秒
131.
Panax japonicus is one of the important medicinal plants. Here, we established the protocol for plant regeneration of P. japonicus via direct somatic embryogenesis. Somatic embryos were directly obtained from the segments of zygotic embryos on MS medium
with 4.4 μM 2,4-D. Thereafter, somatic embryos were produced by repetitive secondary somatic embryogenesis. The secondary
somatic embryo formation was enhanced by plasmolyzing pretreatment (1.0 M mannitol for 10 h). Frequency of secondary somatic
embryo formation from cotyledon segments was lowered by plasmolyzing pretreatment, but the number of somatic embryos per explants
was greatly increased. Plasmolyzing pretreatment resulted in retardation of embryo growth and required subculture to fresh
medium for further growth of embryos into cotyledonary stage. Without plasmolyzing pretreatment, cotyledonary embryos were
obtained after 8 weeks of culture. All the cotyledonary somatic embryos germinated by 5 μM GA3 treatment, but only 15.3% were germinated on hormone-free medium. After 2 months of culture on 1/2 strength WPM medium, plantlets
produced flowers spontaneously. In the anthers of in vitro flowers, microsporogenesis occurred normally with low number of
pollen grains. 相似文献
132.
Background
Pten functionally acts as a tumor suppressor gene. Lately, tissue-specific ablation of Pten gene in mice has elucidated the role of Pten in different tumor progression models. However, a temporally controlled Pten loss in all adult tissues to examine susceptibility of various tissues to Pten-deficient tumorigenesis has not been addressed yet. Our goal was to explore the genesis of Pten-deficient malignancies in multiple tissue lineages of the adult mouse.Methods and Findings
We utilized an inducible Cre/loxP system to delete Pten exon 5 in the systemic organs of ROSA26 (R26)-CreERT;Ptenfx/fx mice. On reaching 45 weeks 4OHT-induced Pten loss, we found that the R26-CreERT;Ptenfx/fx mice developed a variety of malignancies. Overall tumor mean latency was 17 weeks in the Pten-deficient mice. Interestingly, mutant females developed malignancies more quickly at 10∼11 weeks compared with a tumor latency of 21 weeks for mutant males. Lymphoma incidence (76.9% in females; 40.0% in males) was higher than the other malignancies found in the mutant mice. Mutant males developed prostate (20.0%), intestinal cancer (35.0%) and squamous cell carcinoma (10.0%), whereas the mutant females developed squamous cell carcinoma (15.4%) and endometrial cancer (46.1%) in addition to lymphomas. Furthermore, we tested the pharmacological inhibition of the PTEN downstream effectors using on Pten-deficient prostate hyperplasia. Our data revealed that, indeed, the prostate hyperplasia resulting from the induced Pten loss was significantly suppressed by LY294002 (p = 0.007). LY294002Conclusions
Through monitoring a variety of Pten-deficient tumor formation, our results revealed that the lymphoid lineages and the epithelium of the prostate, endometrium, intestine and epidermis are highly susceptible to tumorigenesis after the Pten gene is excised. Therefore, this R26-CreERT; Ptenfx/fx mouse model may provide an entry point for understanding the role of Pten in the tumorigenesis of different organs and extend the search for potential therapeutic approaches to prevent Pten-deficient malignancies. 相似文献133.
You J Zhang H Zhang H Yu A Xiao T Wang Y Song D 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2007,856(1-2):278-284
A method for determining triazine herbicides in infant nutrient cereal-based foods by pressurized microwave-assisted extraction (PMAE), coupled with high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI/MS), is described. The key parameters of PMAE, including extraction solvent, extraction time and temperature, were optimized. The isolation of the target compounds from the matrix was found to be efficient when 2 g of nutrient cereal samples was extracted with 20 mL of methanol for 10 min at 105 degrees C. Final determination was accomplished by HPLC-ESI/MS. The recoveries from 66.2 to 88.6% were obtained for three compounds at fortification levels (5-500 microg kg(-1)) with relative standard deviations (R.S.D.) 相似文献
134.
Luminescence from the triplet probe erythrosin B provides spectroscopic characteristics such as emission energy and lifetime
that are sensitive to molecular mobility of the local solvent environment. This study investigated how variation in glycerol
content influences the properties of an amorphous sucrose matrix by monitoring phosphorescence of erythrosin B over the temperature
range from 5 to 100°C. Emission energy, lifetime, and red-edge excitation data revealed that glycerol affected the mobility
of amorphous sucrose matrix primarily through plasticization when the mole ratio of glycerol/sucrose was above 0.27, resulting
in a decrease in emission energy (ν
p), lifetime (τ) and energy difference (Δν
P) with excitation at the absorption peak and red edge and an increase in the nonradiative, collisional quenching rate k
TS0. At mole ratios ≤0.27 and at temperatures below the matrix T
g, glycerol exhibited an “antiplasticization” effect, as indicated by higher values of emission energy, lifetime, and energy
difference and lower values of the matrix collisional quenching rate. Changes in the distribution of emission energy (emission
bandwidth) and lifetime, and variation in the emission lifetime vs wavelength showed that glycerol reduced the spectral heterogeneity.
These data illustrate the complex effect of a hydrogen bonding solute on the mobility of an amorphous, hydrogen bonded sugar
matrix. 相似文献
135.
136.
UiO-66-NH2 nanocomposite was post-modified with 4-mercaptophenylboronic acid (MPBA) by the method of in situ hybridization reaction. The hybrid boronate affinity material UiO-NH2@P (TEPIC-co-MPBA) was characterized by scanning electron microscopy, X-ray diffraction and Fourier-transform infrared spectroscopy. The material was applied as fluorescent probe for the detection of cis-diol containing compounds based on the boronate affinity mechanism, and exhibited high specific selectively. The proposed method exhibited good linearity for the detection of catechol in the range of 0.50 to 8.00 μg ml−1. The detection limit was 0.13 μg ml−1. The tactic was successfully applied to analyze the total polyphenols in tea beverages for catechol, and relative recovery was in 98.86–106.00%. Therefore, this work provided a promising strategy for the recognition of cis-diol containing compounds. 相似文献
137.
138.
Wenping Wang Xiaoxv Dong Longtai You Na Sai Xin Leng Chunjing Yang Xingbin Yin Jian Ni 《Journal of cellular physiology》2019,234(5):7078-7089
Rhizoma Paridis, a traditional Chinese medicine, has shown promise in cancer prevention and therapy. Polyphyllin II is one of the most significant saponins in Rhizoma Paridis and it has toxic effects on kinds of cancer cells. However, our results in this study proved that the polyphyllin II has hepatotoxicity in vitro through caspases activation and cell-cycle arrest. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide results indicated polyphyllin II inhibited proliferation, induced apoptosis in HepaRG cells and HL-7702 cells and showed a concentration and time-dependent. Then, we selected the innovative cell model-HepaRG cells to explore the mechanism of hepatotoxicity. Our data showed the reactive oxygen species (ROS) increased and the mitochondrial membrane potential decreased in HepaRG cells after administration of polyphyllin II. Besides, with the increase of concentration, the release of lactate dehydrogenase increased and the S phase of the cell cycle was arrested. Nevertheless, when pretreatment with antioxidant N-acetylcysteine, apoptotic cells decreased significantly, inhibited the production of ROS and improved the decrease of membrane potential in HepaRG cells. Moreover, polyphyllin II treatment increased levels of Fas, Bax, cytochrome c, activated caspase-3, -8, -9, cleaved poly(ADP-ribose) polymerase and decreased Bcl-2 expression levels. Finally, we identified two signal pathways of apoptosis induced by polyphyllin II including the death receptor pathway and the mitochondria pathway. This study confirmed the hepatotoxicity of the polyphyllin II in vitro, which has never been discovered and gave a wake-up call for the clinical application of Rhizoma Paridis. 相似文献
139.
The wave wash hunting employed by Orcinus orca, also known as killer whales, is unique in that the prey is hunted outside of the water by generating waves. To quantitatively analyze the specific mechanism of the wave wash, data were obtained using computational fluid dynamics (CFD), and wave theory was introduced as the theoretical background to clarify the mechanism. The relationships between the swimming characteristics and wave parameters are defined in this paper. The results obtained by numerical investigation revealed that the wavelength increased with the swimming speed. Additionally, the wave height increased as the swimming speed increased and the swimming depth became shallower, and subsequently converged to a maximum of 2.42 m. The success of hunting is determined by two wave parameters, which indicate the intensity of the wave wash: the wave height and force exerted on the prey. The metabolic rate and the drag force are considered to evaluate the efficiency of the locomotion, which varied according to the swimming speed (V) and swimming depth (d) of the whales. To generate hunting waves efficiently, the optimal ranges of V and d were estimated to be 3 ~ 5 m/s and 0.5 m ~ 1.1 m respectively. 相似文献
140.
Yue Jianmin You Yanhuang Zhang Liang Fu Zhiyuan Wang Jinping Zhang Jinchi Guy Robert D. 《Journal of Plant Growth Regulation》2019,38(2):669-682
Journal of Plant Growth Regulation - The brassinosteroids (BRs) constitute a recently defined class of plant hormone that can enhance the resistance of plants to multiple stresses. However, the... 相似文献